diff --git a/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Mentoring.java b/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Mentoring.java
index c8ccd00b..af7e476d 100644
--- a/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Mentoring.java
+++ b/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Mentoring.java
@@ -52,7 +52,12 @@ public void updateTags(List<Tag> tags) {
 
         if (tags != null) {
             tags.forEach(tag ->
-                this.mentoringTags.add(new MentoringTag(this, tag))
+                this.mentoringTags.add(
+                    MentoringTag.builder()
+                        .mentoring(this)
+                        .tag(tag)
+                        .build()
+                )
             );
         }
     }
diff --git a/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Tag.java b/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Tag.java
index 6520868d..b4271246 100644
--- a/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Tag.java
+++ b/back/src/main/java/com/back/domain/mentoring/mentoring/entity/Tag.java
@@ -11,7 +11,7 @@
 @Getter
 @NoArgsConstructor
 public class Tag extends BaseEntity {
-    @Column(length = 50, nullable = false, unique = true)
+    @Column(length = 50, nullable = false)
     private String name;
 
     @Builder
diff --git a/back/src/main/java/com/back/domain/mentoring/mentoring/service/MentoringService.java b/back/src/main/java/com/back/domain/mentoring/mentoring/service/MentoringService.java
index b177a08b..e3487cc8 100644
--- a/back/src/main/java/com/back/domain/mentoring/mentoring/service/MentoringService.java
+++ b/back/src/main/java/com/back/domain/mentoring/mentoring/service/MentoringService.java
@@ -24,7 +24,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Set;
+import java.util.Map;
 import java.util.stream.Collectors;
 
 @Service
@@ -123,33 +123,51 @@ private List<Tag> getOrCreateTags(List<String> tagNames) {
             return new ArrayList<>();
         }
 
-        // 기존 태그 조회
-        List<Tag> existingTags = tagRepository.findByNameIn(tagNames);
-
-        Set<String> existingNames = existingTags.stream()
-            .map(Tag::getName)
-            .collect(Collectors.toSet());
+        // 1. 동일한 사용자의 태그 중복 제거
+        List<String> distinctNames = tagNames.stream()
+            .map(String::trim)
+            .filter(name -> !name.isEmpty())
+            .distinct()
+            .toList();
 
-        // 신규 태그 생성
-        List<Tag> newTags = createNewTags(tagNames, existingNames);
+        // 2. 기존 태그 조회 - MySQL collation에 의해 대소문자 무시
+        Map<String, Tag> tagMap = tagRepository.findByNameIn(distinctNames).stream()
+            .collect(Collectors.toMap(
+                Tag::getName,
+                tag -> tag, (t1, t2) -> t1)
+            );
 
-        // 기존 태그 + 신규 태그
-        List<Tag> allTags = new ArrayList<>(existingTags);
-        allTags.addAll(newTags);
+        return buildTagList(distinctNames, tagMap);
+    }
 
-        return allTags;
+    /**
+     * 기존 태그 + 신규 태그
+     * - 정확히 일치하는 건 재사용 (대소문자 구분)
+     * - 없을 경우 신규 태그 생성
+     */
+    private List<Tag> buildTagList(List<String> distinctNames, Map<String, Tag> tagMap) {
+        List<Tag> result = new ArrayList<>();
+        for (String name : distinctNames) {
+            Tag tag = tagMap.getOrDefault(name, createTagSafely(name));
+            if (tag != null) {
+                result.add(tag);
+            }
+        }
+        return result;
     }
 
-    private List<Tag> createNewTags(List<String> tagNames, Set<String> existingNames) {
-        List<Tag> newTags = tagNames.stream()
-            .filter(name -> !existingNames.contains(name))
-            .map(name -> Tag.builder().name(name).build())
-            .toList();
+    private Tag createTagSafely(String name) {
+        // 생성 전 재조회로 중복 방지
+        Tag existing = tagRepository.findByNameIn(List.of(name)).stream()
+            .filter(tag -> tag.getName().equals(name))
+            .findFirst()
+            .orElse(null);
 
-        if (!newTags.isEmpty()) {
-            tagRepository.saveAll(newTags);
+        if (existing != null) {
+            return existing;
         }
-        return newTags;
+
+        return tagRepository.save(Tag.builder().name(name).build());
     }
 
 
diff --git a/back/src/main/java/com/back/domain/mentoring/reservation/service/ReservationService.java b/back/src/main/java/com/back/domain/mentoring/reservation/service/ReservationService.java
index 793bd01e..72184e3b 100644
--- a/back/src/main/java/com/back/domain/mentoring/reservation/service/ReservationService.java
+++ b/back/src/main/java/com/back/domain/mentoring/reservation/service/ReservationService.java
@@ -71,24 +71,28 @@ public ReservationResponse getReservation(Member member, Long reservationId) {
 
     @Transactional
     public ReservationResponse createReservation(Mentee mentee, ReservationRequest reqDto) {
-        Mentoring mentoring = mentoringStorage.findMentoring(reqDto.mentoringId());
-        MentorSlot mentorSlot = mentoringStorage.findMentorSlot(reqDto.mentorSlotId());
+        try {
+            Mentoring mentoring = mentoringStorage.findMentoring(reqDto.mentoringId());
+            MentorSlot mentorSlot = mentoringStorage.findMentorSlot(reqDto.mentorSlotId());
 
-        DateTimeValidator.validateStartTimeNotInPast(mentorSlot.getStartDateTime());
-        validateMentorSlotStatus(mentorSlot, mentee);
-        validateOverlappingTimeForMentee(mentee, mentorSlot);
+            DateTimeValidator.validateStartTimeNotInPast(mentorSlot.getStartDateTime());
+            validateMentorSlotStatus(mentorSlot, mentee);
+            validateOverlappingTimeForMentee(mentee, mentorSlot);
 
-        Reservation reservation = Reservation.builder()
-            .mentoring(mentoring)
-            .mentee(mentee)
-            .mentorSlot(mentorSlot)
-            .preQuestion(reqDto.preQuestion())
-            .build();
-        reservationRepository.save(reservation);
+            Reservation reservation = Reservation.builder()
+                .mentoring(mentoring)
+                .mentee(mentee)
+                .mentorSlot(mentorSlot)
+                .preQuestion(reqDto.preQuestion())
+                .build();
+            reservationRepository.save(reservation);
 
-        mentorSlot.updateStatus(MentorSlotStatus.PENDING);
+            mentorSlot.updateStatus(MentorSlotStatus.PENDING);
 
-        return ReservationResponse.from(reservation);
+            return ReservationResponse.from(reservation);
+        } catch (OptimisticLockException e) {
+            throw new ServiceException(ReservationErrorCode.CONCURRENT_RESERVATION_CONFLICT);
+        }
     }
 
     @Transactional