diff --git a/src/main/java/com/sb/web/account/domain/AccountCategory.java b/src/main/java/com/sb/web/account/domain/AccountCategory.java
index f124e53..33d8649 100644
--- a/src/main/java/com/sb/web/account/domain/AccountCategory.java
+++ b/src/main/java/com/sb/web/account/domain/AccountCategory.java
@@ -21,6 +21,7 @@ public class AccountCategory implements Serializable {
     private Long memberId;
     private String type;   // INCOME / EXPENSE
     private String name;
+    private Long parentId; // 대분류 id (NULL=대분류, 값=소분류)
     private Integer sortOrder;
     private LocalDateTime createdAt;
 }
diff --git a/src/main/java/com/sb/web/account/dto/CategoryRequest.java b/src/main/java/com/sb/web/account/dto/CategoryRequest.java
index 21bb17d..1e83aba 100644
--- a/src/main/java/com/sb/web/account/dto/CategoryRequest.java
+++ b/src/main/java/com/sb/web/account/dto/CategoryRequest.java
@@ -18,4 +18,7 @@ public class CategoryRequest {
     @NotBlank(message = "분류 이름을 입력하세요.")
     @Size(max = 50, message = "분류 이름은 50자 이내여야 합니다.")
     private String name;
+
+    /** 대분류 id. null=대분류로 생성, 값=해당 대분류의 소분류로 생성/이동 */
+    private Long parentId;
 }
diff --git a/src/main/java/com/sb/web/account/dto/CategoryResponse.java b/src/main/java/com/sb/web/account/dto/CategoryResponse.java
index 73eb086..980f534 100644
--- a/src/main/java/com/sb/web/account/dto/CategoryResponse.java
+++ b/src/main/java/com/sb/web/account/dto/CategoryResponse.java
@@ -14,8 +14,11 @@ public class CategoryResponse {
     private Long id;
     private String type;
     private String name;
+    private Long parentId; // 대분류 id (null=대분류)
 
     public static CategoryResponse from(AccountCategory c) {
-        return CategoryResponse.builder().id(c.getId()).type(c.getType()).name(c.getName()).build();
+        return CategoryResponse.builder()
+                .id(c.getId()).type(c.getType()).name(c.getName()).parentId(c.getParentId())
+                .build();
     }
 }
diff --git a/src/main/java/com/sb/web/account/mapper/CategoryMapper.java b/src/main/java/com/sb/web/account/mapper/CategoryMapper.java
index 3236e92..c15e2be 100644
--- a/src/main/java/com/sb/web/account/mapper/CategoryMapper.java
+++ b/src/main/java/com/sb/web/account/mapper/CategoryMapper.java
@@ -16,6 +16,9 @@ public interface CategoryMapper {
 
     AccountCategory findByIdAndMember(@Param("id") Long id, @Param("memberId") Long memberId);
 
+    /** 해당 대분류(parent_id)에 속한 소분류 개수 */
+    int countChildren(@Param("memberId") Long memberId, @Param("parentId") Long parentId);
+
     int countByName(@Param("memberId") Long memberId,
                     @Param("type") String type,
                     @Param("name") String name,
diff --git a/src/main/java/com/sb/web/account/service/CategoryService.java b/src/main/java/com/sb/web/account/service/CategoryService.java
index c311137..69e53a9 100644
--- a/src/main/java/com/sb/web/account/service/CategoryService.java
+++ b/src/main/java/com/sb/web/account/service/CategoryService.java
@@ -35,14 +35,30 @@ public class CategoryService {
         if (categoryMapper.countByName(memberId, req.getType(), name, null) > 0) {
             throw new ApiException(HttpStatus.CONFLICT, "이미 존재하는 분류입니다.");
         }
+        validateParent(req.getParentId(), req.getType(), memberId);
         Integer max = categoryMapper.maxSortOrder(memberId, req.getType());
         int order = (max == null ? 0 : max + 1);
         AccountCategory c = AccountCategory.builder()
-                .memberId(memberId).type(req.getType()).name(name).sortOrder(order).build();
+                .memberId(memberId).type(req.getType()).name(name)
+                .parentId(req.getParentId()).sortOrder(order).build();
         categoryMapper.insert(c);
         return CategoryResponse.from(c);
     }
 
+    /** 대분류 지정 검증: null=대분류 / 값=대분류여야(2단계 제한·동일타입·본인) */
+    private void validateParent(Long parentId, String type, Long memberId) {
+        if (parentId == null) {
+            return;
+        }
+        AccountCategory parent = categoryMapper.findByIdAndMember(parentId, memberId);
+        if (parent == null || !parent.getType().equals(type)) {
+            throw new ApiException(HttpStatus.BAD_REQUEST, "대분류가 올바르지 않습니다.");
+        }
+        if (parent.getParentId() != null) {
+            throw new ApiException(HttpStatus.BAD_REQUEST, "대분류 아래에만 소분류를 둘 수 있습니다(2단계).");
+        }
+    }
+
     /** 드래그앤드랍 순서 변경: 전달된 id 순서대로 sort_order 재설정 (본인·동일 타입만) */
     @Transactional
     public List<CategoryResponse> reorder(Long memberId, String type, List<Long> ids) {
@@ -56,7 +72,8 @@ public class CategoryService {
         return list(memberId);
     }
 
-    /** 이름만 변경 가능. 변경 시 기존 내역·예산의 분류명도 함께 갱신 */
+    /** 이름 변경 + 대분류 이동. 이름 변경 시 기존 내역·예산의 분류명도 함께 갱신.
+     *  주의: parentId 는 항상 현재값(또는 새 대분류)을 보내야 한다(미전송 시 대분류로 풀림). */
     @Transactional
     public CategoryResponse update(Long id, CategoryRequest req, Long memberId) {
         AccountCategory c = mustFind(id, memberId);
@@ -64,8 +81,20 @@ public class CategoryService {
         if (categoryMapper.countByName(memberId, c.getType(), newName, id) > 0) {
             throw new ApiException(HttpStatus.CONFLICT, "이미 존재하는 분류입니다.");
         }
+        Long newParent = req.getParentId();
+        if (newParent != null) {
+            if (newParent.equals(id)) {
+                throw new ApiException(HttpStatus.BAD_REQUEST, "자기 자신을 대분류로 지정할 수 없습니다.");
+            }
+            // 소분류를 가진 대분류는 소분류로 바꿀 수 없음(3단계 방지)
+            if (categoryMapper.countChildren(memberId, id) > 0) {
+                throw new ApiException(HttpStatus.BAD_REQUEST, "소분류가 있는 대분류는 소분류로 바꿀 수 없습니다.");
+            }
+        }
+        validateParent(newParent, c.getType(), memberId);
         String oldName = c.getName();
         c.setName(newName);
+        c.setParentId(newParent);
         categoryMapper.update(c);
         if (!oldName.equals(newName)) {
             entryMapper.renameCategory(memberId, c.getType(), oldName, newName);
@@ -79,6 +108,9 @@ public class CategoryService {
     @Transactional
     public void delete(Long id, Long memberId) {
         mustFind(id, memberId);
+        if (categoryMapper.countChildren(memberId, id) > 0) {
+            throw new ApiException(HttpStatus.BAD_REQUEST, "소분류가 있는 대분류는 삭제할 수 없습니다. 소분류를 먼저 옮기거나 삭제하세요.");
+        }
         categoryMapper.delete(id, memberId);
     }
 
diff --git a/src/main/resources/db/account.sql b/src/main/resources/db/account.sql
index 23f86d9..60e85c5 100644
--- a/src/main/resources/db/account.sql
+++ b/src/main/resources/db/account.sql
@@ -104,12 +104,16 @@ CREATE TABLE IF NOT EXISTS account_category (
     member_id  BIGINT      NOT NULL COMMENT '소유자 member.id',
     type       VARCHAR(10) NOT NULL COMMENT 'INCOME / EXPENSE',
     name       VARCHAR(50) NOT NULL,
+    parent_id  BIGINT      NULL COMMENT '대분류 id(account_category.id). NULL=대분류, 값=소분류',
     sort_order INT         NOT NULL DEFAULT 0,
     created_at DATETIME    NOT NULL DEFAULT CURRENT_TIMESTAMP,
     PRIMARY KEY (id),
     UNIQUE KEY uk_category_member_type_name (member_id, type, name)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
+-- 대/소분류 계층 추가(기존 DB 마이그레이션) — 소분류 이름은 그대로, parent_id 만 부여
+ALTER TABLE account_category ADD COLUMN IF NOT EXISTS parent_id BIGINT NULL COMMENT '대분류 id. NULL=대분류, 값=소분류';
+
 -- 예산 (사용자별, 카테고리별)
 -- fixed=1(고정): base_unit/base_amount 로 일수기준 환산 / fixed=0(비고정): daily/weekly/monthly/yearly 직접
 CREATE TABLE IF NOT EXISTS budget (
diff --git a/src/main/resources/mapper/CategoryMapper.xml b/src/main/resources/mapper/CategoryMapper.xml
index c64d4bf..c242bcf 100644
--- a/src/main/resources/mapper/CategoryMapper.xml
+++ b/src/main/resources/mapper/CategoryMapper.xml
@@ -8,23 +8,29 @@
         <result property="memberId" column="member_id"/>
         <result property="type" column="type"/>
         <result property="name" column="name"/>
+        <result property="parentId" column="parent_id"/>
         <result property="sortOrder" column="sort_order"/>
         <result property="createdAt" column="created_at"/>
     </resultMap>
 
     <select id="findByMember" parameterType="long" resultMap="categoryResultMap">
-        SELECT id, member_id, type, name, sort_order, created_at
+        SELECT id, member_id, type, name, parent_id, sort_order, created_at
         FROM account_category
         WHERE member_id = #{memberId}
         ORDER BY type, sort_order, name
     </select>
 
     <select id="findByIdAndMember" resultMap="categoryResultMap">
-        SELECT id, member_id, type, name, sort_order, created_at
+        SELECT id, member_id, type, name, parent_id, sort_order, created_at
         FROM account_category
         WHERE id = #{id} AND member_id = #{memberId}
     </select>
 
+    <select id="countChildren" resultType="int">
+        SELECT COUNT(*) FROM account_category
+        WHERE member_id = #{memberId} AND parent_id = #{parentId}
+    </select>
+
     <select id="countByName" resultType="int">
         SELECT COUNT(*) FROM account_category
         WHERE member_id = #{memberId} AND type = #{type} AND name = #{name}
@@ -33,17 +39,17 @@
 
     <insert id="insert" parameterType="com.sb.web.account.domain.AccountCategory"
             useGeneratedKeys="true" keyProperty="id">
-        INSERT INTO account_category (member_id, type, name, sort_order, created_at)
-        VALUES (#{memberId}, #{type}, #{name}, #{sortOrder}, NOW())
+        INSERT INTO account_category (member_id, type, name, parent_id, sort_order, created_at)
+        VALUES (#{memberId}, #{type}, #{name}, #{parentId}, #{sortOrder}, NOW())
     </insert>
 
     <insert id="insertIgnore" parameterType="com.sb.web.account.domain.AccountCategory">
-        INSERT IGNORE INTO account_category (member_id, type, name, sort_order, created_at)
-        VALUES (#{memberId}, #{type}, #{name}, 0, NOW())
+        INSERT IGNORE INTO account_category (member_id, type, name, parent_id, sort_order, created_at)
+        VALUES (#{memberId}, #{type}, #{name}, #{parentId}, 0, NOW())
     </insert>
 
     <update id="update" parameterType="com.sb.web.account.domain.AccountCategory">
-        UPDATE account_category SET name = #{name}
+        UPDATE account_category SET name = #{name}, parent_id = #{parentId}
         WHERE id = #{id} AND member_id = #{memberId}
     </update>