diff --git a/src/main/java/io/oeid/mogakgo/domain/project/application/ProjectService.java b/src/main/java/io/oeid/mogakgo/domain/project/application/ProjectService.java
index 4233ba2d..7c4e0e3e 100644
--- a/src/main/java/io/oeid/mogakgo/domain/project/application/ProjectService.java
+++ b/src/main/java/io/oeid/mogakgo/domain/project/application/ProjectService.java
@@ -28,7 +28,6 @@
 import io.oeid.mogakgo.domain.user.domain.User;
 import io.oeid.mogakgo.domain.user.exception.UserException;
 import io.oeid.mogakgo.domain.user.infrastructure.UserJpaRepository;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
@@ -77,11 +76,6 @@ public Long create(Long userId, ProjectCreateReq request) {
         return project.getId();
     }
 
-    private boolean isExistsNotEndProjectCard(User tokenUser) {
-        return !projectJpaRepository.findNotEndProjectOneByCreatorId(tokenUser.getId(),
-            PageRequest.of(0, 1)).isEmpty();
-    }
-
     @Transactional
     public void delete(Long userId, Long projectId) {
         // 유저 존재 여부 체크
@@ -94,6 +88,7 @@ public void delete(Long userId, Long projectId) {
         project.delete(user);
     }
 
+    @Transactional
     public void cancel(Long userId, Long projectId) {
         // 유저 존재 여부 체크
         User user = getUser(userId);
@@ -106,6 +101,9 @@ public void cancel(Long userId, Long projectId) {
 
         // 프로젝트 취소
         project.cancel(user, projectHasReq);
+
+        // 프로젝트가 받은 모든 요청 거절
+        projectJoinRequestJpaRepository.rejectAllByProjectId(projectId);
     }
 
     public CursorPaginationResult<projectJoinRequestRes> getJoinRequest(
@@ -160,6 +158,11 @@ public ProjectDensityRankRes getDensityRankProjects() {
         return new ProjectDensityRankRes(regionRankList);
     }
 
+    private boolean isExistsNotEndProjectCard(User tokenUser) {
+        return !projectJpaRepository.findNotEndProjectOneByCreatorId(tokenUser.getId(),
+            PageRequest.of(0, 1)).isEmpty();
+    }
+
     private void fillWithDefaultRegionsIfNecessary(List<Region> regionRankList) {
         if (regionRankList.size() < DENSITY_RANK_LIMIT) {
             // 기본 지역 순위에서 이미 리스트에 있는 지역을 제외하고 남은 지역을 추가
diff --git a/src/main/java/io/oeid/mogakgo/domain/project_join_req/infrastructure/ProjectJoinRequestJpaRepository.java b/src/main/java/io/oeid/mogakgo/domain/project_join_req/infrastructure/ProjectJoinRequestJpaRepository.java
index 3fed8eef..3b35d79c 100644
--- a/src/main/java/io/oeid/mogakgo/domain/project_join_req/infrastructure/ProjectJoinRequestJpaRepository.java
+++ b/src/main/java/io/oeid/mogakgo/domain/project_join_req/infrastructure/ProjectJoinRequestJpaRepository.java
@@ -4,6 +4,7 @@
 import java.util.Optional;
 import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
 
 public interface ProjectJoinRequestJpaRepository extends JpaRepository<ProjectJoinRequest, Long>,
@@ -23,4 +24,8 @@ public interface ProjectJoinRequestJpaRepository extends JpaRepository<ProjectJo
     @Query("select pjr from ProjectJoinRequest pjr where pjr.sender.id = :userId")
     Optional<ProjectJoinRequest> findAlreadyExistsAnotherJoinReq(Long userId);
 
+    @Modifying
+    @Query("update ProjectJoinRequest pjr set pjr.requestStatus = 'REJECTED' where pjr.project.id = :projectId and pjr.requestStatus = 'PENDING'")
+    int rejectAllByProjectId(Long projectId);
+
 }