diff --git a/modules/document/document.class.php b/modules/document/document.class.php
index 0d2eef81d..5a2fe043c 100644
--- a/modules/document/document.class.php
+++ b/modules/document/document.class.php
@@ -105,6 +105,10 @@ class Document extends ModuleObject
 		// 2017.12.21 Add an index for nick_name
 		if(!$oDB->isIndexExists('documents', 'idx_nick_name')) return true;
 
+		// 2024.05.04 Add default category
+		if(!$oDB->isColumnExists('document_categories', 'is_default')) return true;
+		if(!$oDB->isIndexExists('document_categories', 'idx_list_order')) return true;
+
 		return false;
 	}
 
@@ -205,6 +209,16 @@ class Document extends ModuleObject
 		{
 			$oDB->addIndex('documents', 'idx_nick_name', array('nick_name'));
 		}
+
+		// 2024.05.04 Add default category
+		if(!$oDB->isColumnExists('document_categories', 'is_default'))
+		{
+			$oDB->addColumn('document_categories', 'is_default', 'char', '1', 'N', true, 'expand');
+		}
+		if(!$oDB->isIndexExists('document_categories', 'idx_list_order'))
+		{
+			$oDB->addIndex('document_categories', 'idx_list_order', array('list_order'));
+		}
 	}
 
 	/**
diff --git a/modules/document/document.controller.php b/modules/document/document.controller.php
index d4e93ede4..73019c943 100644
--- a/modules/document/document.controller.php
+++ b/modules/document/document.controller.php
@@ -2565,26 +2565,33 @@ class DocumentController extends Document
 	function procDocumentInsertCategory($args = null)
 	{
 		// List variables
-		if(!$args) $args = Context::gets('module_srl','category_srl','parent_srl','category_title','category_description','expand','group_srls','category_color','mid');
+		if(!$args) $args = Context::gets('module_srl','category_srl','parent_srl','category_title','category_description','expand','is_default','group_srls','category_color','mid');
 		$args->title = trim($args->category_title);
 		$args->description = trim($args->category_description);
 		$args->color = $args->category_color;
+		$args->expand = (isset($args->expand) && $args->expand === 'Y') ? 'Y' : 'N';
+		$args->is_default = (isset($args->is_default) && $args->is_default === 'Y') ? 'Y' : 'N';
 
 		if(!$args->module_srl && $args->mid)
 		{
-			$mid = $args->mid;
 			unset($args->mid);
 			$args->module_srl = $this->module_srl;
 		}
+
 		// Check permissions
 		$columnList = array('module_srl', 'module');
 		$module_info = ModuleModel::getModuleInfoByModuleSrl($args->module_srl, $columnList);
 		$grant = ModuleModel::getGrant($module_info, Context::get('logged_info'));
 		if(!$grant->manager) return new BaseObject(-1, 'msg_not_permitted');
 
-		if($args->expand !="Y") $args->expand = "N";
-		if(!is_array($args->group_srls)) $args->group_srls = str_replace('|@|',',',$args->group_srls);
-		else $args->group_srls = implode(',', $args->group_srls);
+		if (!is_array($args->group_srls))
+		{
+			$args->group_srls = str_replace('|@|',',',$args->group_srls);
+		}
+		else
+		{
+			$args->group_srls = implode(',', $args->group_srls);
+		}
 		$args->parent_srl = (int)$args->parent_srl;
 
 		$oDB = DB::getInstance();
@@ -2596,6 +2603,7 @@ class DocumentController extends Document
 			$category_info = DocumentModel::getCategory($args->category_srl);
 			if($category_info->category_srl != $args->category_srl) $args->category_srl = null;
 		}
+
 		// Update if exists
 		if($args->category_srl)
 		{
@@ -2616,6 +2624,16 @@ class DocumentController extends Document
 				return $output;
 			}
 		}
+
+		// If set as default, set other categories as not default.
+		if ($args->is_default === 'Y')
+		{
+			$output = executeQuery('document.updateCategoryIsDefault', [
+				'module_srl' => $args->module_srl,
+				'except_category_srl' => $args->category_srl,
+			]);
+		}
+
 		// Update the xml file and get its location
 		$xml_file = $this->makeCategoryFile($args->module_srl);
 
@@ -2890,7 +2908,8 @@ class DocumentController extends Document
 				$child_buff = $this->getXmlTree($tree[$category_srl], $tree, $site_srl, $xml_header_buff);
 			}
 			// List variables
-			$expand = ($node->expand) ? $node->expand : 'N';
+			$expand = isset($node->expand) ? $node->expand : 'N';
+			$is_default = isset($node->is_default) ? $node->is_default : 'N';
 			$group_srls = ($node->group_srls) ? $node->group_srls : '';
 			$mid = ($node->mid) ? $node->mid : '';
 			$module_srl = ($node->module_srl) ? $node->parent_srl : '';
@@ -2923,7 +2942,7 @@ class DocumentController extends Document
 			}
 
 			$attribute = sprintf(
-				'mid="%s" module_srl="%d" node_srl="%d" parent_srl="%d" category_srl="%d" text="<?php echo (%s?($_titles[%d][$lang_type]):"")?>" url=%s expand=%s color=%s description="<?php echo (%s?($_descriptions[%d][$lang_type]):"")?>" document_count="%d" ',
+				'mid="%s" module_srl="%d" node_srl="%d" parent_srl="%d" category_srl="%d" text="<?php echo (%s?($_titles[%d][$lang_type]):"")?>" url=%s expand=%s is_default=%s color=%s description="<?php echo (%s?($_descriptions[%d][$lang_type]):"")?>" document_count="%d" ',
 				$mid,
 				$module_srl,
 				$category_srl,
@@ -2933,6 +2952,7 @@ class DocumentController extends Document
 				$category_srl,
 				str_replace("'", '"', var_export(getUrl('','mid',$node->mid,'category',$category_srl), true)),
 				str_replace("'", '"', var_export($expand, true)),
+				str_replace("'", '"', var_export($is_default, true)),
 				str_replace("'", '"', var_export(escape($color, false), true)),
 				$group_check_code,
 				$category_srl,
@@ -2988,7 +3008,8 @@ class DocumentController extends Document
 			// List variables
 			$selected = '"' . implode('","', $child_output['category_srl_list']) . '"';
 			$child_buff = $child_output['buff'];
-			$expand = $node->expand;
+			$expand = $node->expand ?? 'N';
+			$is_default = $node->is_default ?? 'N';
 
 			$title = $node->title;
 			$description = $node->description;
@@ -3027,7 +3048,7 @@ class DocumentController extends Document
 
 			// Create attributes(Use the category_srl_list to check whether to belong to the menu's node. It seems to be tricky but fast fast and powerful;)
 			$attribute = sprintf(
-				'"mid" => "%s", "module_srl" => "%d","node_srl"=>"%d","category_srl"=>"%d","parent_srl"=>"%d","text"=>$_titles[%d][$lang_type],"selected"=>(in_array(Context::get("category"),array(%s))?1:0),"expand"=>%s,"color"=>%s,"description"=>$_descriptions[%d][$lang_type],"list"=>array(%s),"document_count"=>"%d","grant"=>%s?true:false',
+				'"mid" => "%s", "module_srl" => "%d","node_srl"=>"%d","category_srl"=>"%d","parent_srl"=>"%d","text"=>$_titles[%d][$lang_type],"selected"=>(in_array(Context::get("category"),array(%s))?1:0),"expand"=>%s,"is_default"=>%s,"color"=>%s,"description"=>$_descriptions[%d][$lang_type],"list"=>array(%s),"document_count"=>"%d","grant"=>%s?true:false',
 				$node->mid,
 				$node->module_srl,
 				$node->category_srl,
@@ -3036,6 +3057,7 @@ class DocumentController extends Document
 				$node->category_srl,
 				$selected,
 				var_export($expand, true),
+				var_export($is_default, true),
 				var_export($node->color, true),
 				$node->category_srl,
 				$child_buff,
diff --git a/modules/document/document.model.php b/modules/document/document.model.php
index 3195eef51..a3c2932da 100644
--- a/modules/document/document.model.php
+++ b/modules/document/document.model.php
@@ -813,7 +813,8 @@ class DocumentModel extends Document
 			$obj->parent_srl = $val['parent_srl'];
 			$obj->title = $obj->text = $val['text'];
 			$obj->description = $val['description'];
-			$obj->expand = $val['expand']=='Y'?true:false;
+			$obj->expand = isset($val['expand']) && $val['expand'] === 'Y';
+			$obj->is_default = isset($val['is_default']) && $val['is_default'] === 'Y';
 			$obj->color = $val['color'];
 			$obj->document_count = $val['document_count'];
 			$obj->depth = $depth;
@@ -821,10 +822,19 @@ class DocumentModel extends Document
 			$obj->childs = array();
 			$obj->grant = $val['grant'];
 
-			if(Context::get('mid') == $obj->mid && Context::get('category') == $obj->category_srl) $selected = true;
-			else $selected = false;
-
-			$obj->selected = $selected;
+			$selected_category = Context::get('category');
+			if (Context::get('mid') == $obj->mid && $selected_category == $obj->category_srl)
+			{
+				$obj->selected = true;
+			}
+			elseif (!isset($selected_category) && $obj->is_default)
+			{
+				$obj->selected = true;
+			}
+			else
+			{
+				$obj->selected = false;
+			}
 
 			$list_order[$idx++] = $obj->category_srl;
 			// If you have a parent category of child nodes apply data
@@ -833,7 +843,10 @@ class DocumentModel extends Document
 				$parent_srl = $obj->parent_srl;
 				$document_count = $obj->document_count;
 				$expand = $obj->expand;
-				if($selected) $expand = true;
+				if ($obj->selected)
+				{
+					$expand = true;
+				}
 
 				while($parent_srl)
 				{
diff --git a/modules/document/lang/en.php b/modules/document/lang/en.php
index 4aa9befd0..281cfba03 100644
--- a/modules/document/lang/en.php
+++ b/modules/document/lang/en.php
@@ -16,12 +16,14 @@ $lang->parent_category_title = 'Parent Category';
 $lang->category_title = 'Category';
 $lang->category_color = 'Category Font Color';
 $lang->expand = 'Expand';
+$lang->is_default_category = 'Default Category';
 $lang->category_group_srls = 'Allowed Groups';
 $lang->cmd_make_child = 'Add Child Category';
 $lang->cmd_enable_move_category = 'Change category position (Select a category and drag it to the position you want.)';
 $lang->about_category_title = 'Please enter a category name.';
 $lang->about_view_count_option = 'This option controls whether to count multiple views by the same user. Different methods will try to detect duplicates in different ways.';
 $lang->about_expand = 'Select this option, and they will stay expanded.';
+$lang->about_default_category = 'Automatically select this category when writing a new post.';
 $lang->about_category_group_srls = 'Only the selected group will be able to write posts in this category. If none is selected, everyone is allowed.';
 $lang->about_category_color = 'You can set the font color of the category. e.g.) red or #ff0000';
 $lang->about_cmd_pc_icon_setting = 'Select the icon set to display next to new or updated articles. The default is \'default\'.';
diff --git a/modules/document/lang/ko.php b/modules/document/lang/ko.php
index b4a7f1f98..1253281a2 100644
--- a/modules/document/lang/ko.php
+++ b/modules/document/lang/ko.php
@@ -16,12 +16,14 @@ $lang->parent_category_title = '상위 분류 명';
 $lang->category_title = '분류 명';
 $lang->category_color = '분류 폰트 색깔';
 $lang->expand = '펼침';
+$lang->is_default_category = '기본 분류';
 $lang->category_group_srls = '작성 허용 그룹';
 $lang->cmd_make_child = '하위 분류 추가';
 $lang->cmd_enable_move_category = '분류 위치 변경 (선택 후 위 메뉴를 드래그하세요.)';
 $lang->about_category_title = '분류 이름을 입력해주세요.';
 $lang->about_view_count_option = '조회 수 설정에 따라 중복 조회 수 카운트를 할 수 있도록 도와줍니다. 각 옵션에 따라 조회 수를 기록하는 방식이 달라집니다.';
 $lang->about_expand = '선택하면 늘 펼쳐진 상태로 있게 합니다.';
+$lang->about_default_category = '글 작성시 이 분류가 기본으로 선택되도록 합니다.';
 $lang->about_category_group_srls = '이 분류를 사용하여 글을 작성할 수 있는 그룹을 제한합니다. 선택하지 않을 경우 모든 사용자에게 허용합니다.';
 $lang->about_category_color = '분류 폰트 색깔을 지정합니다. 예) red 또는 #ff0000';
 $lang->about_cmd_pc_icon_setting = '새로운 글이 등록되었거나 수정되었을 때 출력하는 아이콘입니다. 기본값은 default입니다. 사용 안 함을 선택할 경우 default 스킨이 기본값으로 출력됩니다.';
diff --git a/modules/document/queries/insertCategory.xml b/modules/document/queries/insertCategory.xml
index 442ac1e1b..a18bbcb73 100644
--- a/modules/document/queries/insertCategory.xml
+++ b/modules/document/queries/insertCategory.xml
@@ -5,15 +5,16 @@
     <columns>
         <column name="category_srl" var="category_srl" filter="number" notnull="notnull" />
         <column name="module_srl" var="module_srl" filter="number" default="0" notnull="notnull" />
+        <column name="parent_srl" var="parent_srl" filter="number" default="0" />
         <column name="title" var="title" notnull="notnull" minlength="1" maxlength="250" />
         <column name="description" var="description" maxlength="2000"/>
+        <column name="group_srls" var="group_srls" />
+        <column name="color" var="color" />
+        <column name="expand" var="expand" />
+		<column name="is_default" var="is_default" />
         <column name="document_count" var="document_count" default="0" />
         <column name="regdate" var="regdate" default="curdate()" />
-        <column name="expand" var="expand" />
-        <column name="parent_srl" var="parent_srl" filter="number" default="0" />
-        <column name="group_srls" var="group_srls" />
         <column name="last_update" var="last_update" default="curdate()" />
         <column name="list_order" var="list_order" default="0" />
-        <column name="color" var="color" />
     </columns>
 </query>
diff --git a/modules/document/queries/updateCategory.xml b/modules/document/queries/updateCategory.xml
index 9180af6cb..aa1fae47b 100644
--- a/modules/document/queries/updateCategory.xml
+++ b/modules/document/queries/updateCategory.xml
@@ -5,12 +5,13 @@
     <columns>
         <column name="title" var="title" />
         <column name="description" var="description" />
-        <column name="list_order" var="list_order" />
-        <column name="last_update" var="last_update" default="curdate()" />
-        <column name="expand" var="expand" />
-        <column name="parent_srl" var="parent_srl" filter="number" />
         <column name="group_srls" var="group_srls" />
         <column name="color" var="color" />
+        <column name="expand" var="expand" />
+		<column name="is_default" var="is_default" />
+        <column name="last_update" var="last_update" default="curdate()" />
+        <column name="list_order" var="list_order" />
+        <column name="parent_srl" var="parent_srl" filter="number" />
     </columns>
     <conditions>
         <condition operation="equal" column="category_srl" var="category_srl" filter="number" notnull="notnull" />
diff --git a/modules/document/queries/updateCategoryIsDefault.xml b/modules/document/queries/updateCategoryIsDefault.xml
new file mode 100644
index 000000000..193e8dd43
--- /dev/null
+++ b/modules/document/queries/updateCategoryIsDefault.xml
@@ -0,0 +1,12 @@
+<query id="updateCategoryIsDefault" action="update">
+    <tables>
+        <table name="document_categories" />
+    </tables>
+    <columns>
+        <column name="is_default" var="is_default" default="N" />
+    </columns>
+    <conditions>
+        <condition operation="equal" column="module_srl" var="module_srl" filter="number" notnull="notnull" />
+        <condition operation="notequal" column="category_srl" var="except_category_srl" filter="number" />
+    </conditions>
+</query>
diff --git a/modules/document/schemas/document_categories.xml b/modules/document/schemas/document_categories.xml
index 179d1e50e..7b9f404c7 100644
--- a/modules/document/schemas/document_categories.xml
+++ b/modules/document/schemas/document_categories.xml
@@ -3,12 +3,13 @@
     <column name="module_srl" type="number" notnull="notnull" index="idx_module_srl" />
     <column name="parent_srl" type="number" notnull="notnull" />
     <column name="title" type="varchar" size="250" />
-    <column name="expand" type="char" size="1" default="N" />
-    <column name="document_count" type="number" default="0" notnull="notnull" />
-    <column name="regdate" type="date" index="idx_regdate" />
-    <column name="last_update" type="date" />
-    <column name="list_order" type="number" notnull="notnull" />
+	<column name="description" type="varchar" size="200" />
     <column name="group_srls" type="text" />
     <column name="color" type="varchar" size="11" />
-	<column name="description" type="varchar" size="200" />
+    <column name="expand" type="char" size="1" default="N" notnull="notnull" />
+	<column name="is_default" type="char" size="1" default="N" notnull="notnull" />
+    <column name="document_count" type="number" default="0" notnull="notnull" />
+    <column name="regdate" type="date" notnull="notnull" index="idx_regdate" />
+    <column name="last_update" type="date" />
+    <column name="list_order" type="number" notnull="notnull" index="idx_list_order" />
 </table>
diff --git a/modules/document/tpl/category_list.html b/modules/document/tpl/category_list.html
index e1aa8b36d..80783686b 100644
--- a/modules/document/tpl/category_list.html
+++ b/modules/document/tpl/category_list.html
@@ -83,6 +83,12 @@
 					<label class="x_inline" for="expand"><input type="checkbox" name="expand" value="Y" id="expand" /> {$lang->about_expand}</label>
 				</div>
 			</div>
+			<div class="x_control-group">
+				<label class="x_control-label">{$lang->is_default_category}</label>
+				<div class="x_controls">
+					<label class="x_inline" for="is_default_category"><input type="checkbox" name="is_default" value="Y" id="is_default_category" /> {$lang->about_default_category}</label>
+				</div>
+			</div>
 		</div>
 		<div class="x_modal-footer">
 			<button type="button" class="x_btn x_pull-left" data-hide="#__category_info">{$lang->cmd_close}</button>
diff --git a/modules/document/tpl/js/document_category.js b/modules/document/tpl/js/document_category.js
index 4e99f2732..9d0ad0957 100644
--- a/modules/document/tpl/js/document_category.js
+++ b/modules/document/tpl/js/document_category.js
@@ -210,6 +210,9 @@ function modifyNode(node,e){
 		if(data.category_info.expand == 'Y'){
 			$w.find('input[name="expand"]').attr('checked', 'checked');
 		}
+		if(data.category_info.is_default == 'Y'){
+			$w.find('input[name="is_default"]').attr('checked', 'checked');
+		}
 	});
 
 	$('#__parent_category_info').hide().next('.x_control-group').css('borderTop','0');