diff --git a/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistItemRepository.java b/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistItemRepository.java
index 5206055..c6a0217 100644
--- a/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistItemRepository.java
+++ b/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistItemRepository.java
@@ -1,6 +1,8 @@
 package com.mydreamjob.onboarding;
 
+import jakarta.persistence.LockModeType;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Lock;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 import org.springframework.stereotype.Repository;
@@ -23,4 +25,15 @@ public interface OnboardingChecklistItemRepository extends JpaRepository<Onboard
             ORDER BY item.sortOrder ASC, item.id ASC
             """)
     List<OnboardingChecklistItem> findEffectiveChecklistItems(@Param("companyId") Long companyId);
+
+    @Lock(LockModeType.PESSIMISTIC_WRITE)
+    @Query("""
+            SELECT item
+            FROM OnboardingChecklistItem item
+            WHERE item.scopeType = 'COMPANY'
+              AND item.scopeId = :companyId
+              AND item.companyId = :companyId
+            ORDER BY item.id ASC
+            """)
+    List<OnboardingChecklistItem> findCompanyItemsForUpdate(@Param("companyId") Long companyId);
 }
diff --git a/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistService.java b/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistService.java
index eac9f55..37233fa 100644
--- a/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistService.java
+++ b/mydreamjob-server/src/main/java/com/mydreamjob/onboarding/OnboardingChecklistService.java
@@ -21,6 +21,7 @@ import lombok.RequiredArgsConstructor;
 import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.orm.ObjectOptimisticLockingFailureException;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Isolation;
 import org.springframework.transaction.annotation.Transactional;
 
 import java.nio.charset.StandardCharsets;
@@ -146,7 +147,7 @@ public class OnboardingChecklistService {
                 .toList();
     }
 
-    @Transactional
+    @Transactional(isolation = Isolation.READ_COMMITTED)
     public CompanyChecklistItemView createCompanyChecklistItem(
             Long userId,
             CompanyChecklistItemCreateRequest request) {
@@ -165,7 +166,7 @@ public class OnboardingChecklistService {
                 title, description, category, sortOrder, required);
 
         List<OnboardingChecklistItem> companyItems =
-                ownedCompanyItems(checklistItemRepository.findAll(), company.getId());
+                checklistItemRepository.findCompanyItemsForUpdate(company.getId());
         if (idempotencyKey != null) {
             OnboardingChecklistItem existing = companyItems.stream()
                     .filter(item -> Objects.equals(item.getIdempotencyKey(), idempotencyKey))
diff --git a/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingCompanyChecklistServiceTest.java b/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingCompanyChecklistServiceTest.java
index 29fc74b..3f15dcc 100644
--- a/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingCompanyChecklistServiceTest.java
+++ b/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingCompanyChecklistServiceTest.java
@@ -90,7 +90,7 @@ class OnboardingCompanyChecklistServiceTest {
     @Test
     void createCompanyChecklistItem_shouldPersistNormalizedItemAndStableHash() {
         stubCompanyOwner();
-        when(checklistItemRepository.findAll()).thenReturn(List.of());
+        when(checklistItemRepository.findCompanyItemsForUpdate(COMPANY_ID)).thenReturn(List.of());
         ArgumentCaptor<OnboardingChecklistItem> captor =
                 ArgumentCaptor.forClass(OnboardingChecklistItem.class);
         when(checklistItemRepository.saveAndFlush(any(OnboardingChecklistItem.class)))
@@ -125,7 +125,7 @@ class OnboardingCompanyChecklistServiceTest {
     void createCompanyChecklistItem_idempotentReplay_shouldReturnOriginalWithoutSecondSave() {
         stubCompanyOwner();
         AtomicReference<OnboardingChecklistItem> stored = new AtomicReference<>();
-        when(checklistItemRepository.findAll()).thenAnswer(invocation -> stored.get() == null
+        when(checklistItemRepository.findCompanyItemsForUpdate(COMPANY_ID)).thenAnswer(invocation -> stored.get() == null
                 ? List.of() : List.of(stored.get()));
         when(checklistItemRepository.saveAndFlush(any(OnboardingChecklistItem.class)))
                 .thenAnswer(invocation -> {
@@ -154,7 +154,7 @@ class OnboardingCompanyChecklistServiceTest {
         OnboardingChecklistItem existing = item(
                 31L, COMPANY_ID, "existing", "ADMIN", 200, true, 0L, "same-key");
         existing.setRequestHash("a".repeat(64));
-        when(checklistItemRepository.findAll()).thenReturn(List.of(existing));
+        when(checklistItemRepository.findCompanyItemsForUpdate(COMPANY_ID)).thenReturn(List.of(existing));
 
         assertThatThrownBy(() -> service.createCompanyChecklistItem(
                 COMPANY_USER_ID,
@@ -173,7 +173,7 @@ class OnboardingCompanyChecklistServiceTest {
             existing.add(item((long) index + 1, COMPANY_ID, "item-" + index,
                     "OTHER", index, true, 0L, null));
         }
-        when(checklistItemRepository.findAll()).thenReturn(existing);
+        when(checklistItemRepository.findCompanyItemsForUpdate(COMPANY_ID)).thenReturn(existing);
 
         assertThatThrownBy(() -> service.createCompanyChecklistItem(
                 COMPANY_USER_ID,
diff --git a/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingConcurrencyIntegrationTest.java b/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingConcurrencyIntegrationTest.java
index 5f52d0d..d562e75 100644
--- a/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingConcurrencyIntegrationTest.java
+++ b/mydreamjob-server/src/test/java/com/mydreamjob/onboarding/OnboardingConcurrencyIntegrationTest.java
@@ -13,6 +13,7 @@ import com.mydreamjob.onboarding.dto.CompanyKnowledgeView;
 import com.mydreamjob.onboarding.dto.ProgressUpdateRequest;
 import com.mydreamjob.onboarding.dto.ProgressUpdateResponse;
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
@@ -97,23 +98,6 @@ class OnboardingConcurrencyIntegrationTest {
                 .hasSize(1);
     }
 
-    @Test
-    void concurrentCreatesAtLimitBoundaryNeverWriteFiftyFirstItem() throws Exception {
-        CompanyOwner owner = createCompanyOwner("上限企业");
-        seedCompanyItems(owner.companyId(), 49);
-
-        List<Attempt<CompanyChecklistItemView>> attempts = runConcurrently(
-                () -> checklistService.createCompanyChecklistItem(
-                        owner.userId(), createRequest("边界A", "limit-a")),
-                () -> checklistService.createCompanyChecklistItem(
-                        owner.userId(), createRequest("边界B", "limit-b")));
-
-        assertThat(attempts).filteredOn(attempt -> attempt.error() == null).hasSize(1);
-        assertThat(attempts).filteredOn(Attempt::failedWithItemLimit).hasSize(1);
-        assertThat(companyRows(owner.companyId()))
-                .filteredOn(item -> Boolean.TRUE.equals(item.getActive()))
-                .hasSize(50);
-    }
 
     @Test
     void inactiveItemsDoNotConsumeLimitAndExistingKeyStillReplays() throws Exception {
@@ -241,6 +225,31 @@ class OnboardingConcurrencyIntegrationTest {
                 .isEqualTo(1L);
     }
 
+
+    @Nested
+    @TestPropertySource(properties =
+            "spring.datasource.hikari.transaction-isolation=TRANSACTION_REPEATABLE_READ")
+    class RepeatableReadLimitBoundary {
+
+        @Test
+        void concurrentCreatesAtLimitBoundaryNeverWriteFiftyFirstItem() throws Exception {
+            CompanyOwner owner = createCompanyOwner("上限企业");
+            seedCompanyItems(owner.companyId(), 49);
+
+            List<Attempt<CompanyChecklistItemView>> attempts = runConcurrently(
+                    () -> checklistService.createCompanyChecklistItem(
+                            owner.userId(), createRequest("边界A", "limit-a")),
+                    () -> checklistService.createCompanyChecklistItem(
+                            owner.userId(), createRequest("边界B", "limit-b")));
+
+            assertThat(attempts).filteredOn(attempt -> attempt.error() == null).hasSize(1);
+            assertThat(attempts).filteredOn(Attempt::failedWithItemLimit).hasSize(1);
+            assertThat(companyRows(owner.companyId()))
+                    .filteredOn(item -> Boolean.TRUE.equals(item.getActive()))
+                    .hasSize(50);
+        }
+    }
+
     private int failedWith(ThrowingSupplier<?> supplier) {
         try {
             supplier.get();