diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/controller/ChatRoomController.kt b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/controller/ChatRoomController.kt
index 7be88a4..6f6f10b 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/controller/ChatRoomController.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/controller/ChatRoomController.kt
@@ -1,6 +1,7 @@
 package kr.co.vividnext.sodalive.chat.room.controller
 
 import kr.co.vividnext.sodalive.chat.room.dto.CreateChatRoomRequest
+import kr.co.vividnext.sodalive.chat.room.dto.SendChatMessageRequest
 import kr.co.vividnext.sodalive.chat.room.service.ChatRoomService
 import kr.co.vividnext.sodalive.common.ApiResponse
 import kr.co.vividnext.sodalive.common.SodaException
@@ -116,4 +117,22 @@ class ChatRoomController(
         chatRoomService.leaveChatRoom(member, chatRoomId)
         ApiResponse.ok(true)
     }
+
+    /**
+     * 채팅방 메시지 전송 API
+     * - 참여 여부 검증(미참여시 "잘못된 접근입니다")
+     * - 외부 API 호출 (/api/chat, POST) 재시도 최대 3회
+     * - 성공 시 내 메시지/캐릭터 메시지 저장 후 캐릭터 메시지 리스트 반환
+     */
+    @PostMapping("/{chatRoomId}/send")
+    fun sendMessage(
+        @AuthenticationPrincipal(expression = "#this == 'anonymousUser' ? null : member") member: Member?,
+        @PathVariable chatRoomId: Long,
+        @RequestBody request: SendChatMessageRequest
+    ) = run {
+        if (member == null) throw SodaException("로그인 정보를 확인해주세요.")
+        if (member.auth == null) throw SodaException("본인인증을 하셔야 합니다.")
+
+        ApiResponse.ok(chatRoomService.sendMessage(member, chatRoomId, request.message))
+    }
 }
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/dto/ChatRoomDto.kt b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/dto/ChatRoomDto.kt
index 60ffe61..79bd7cb 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/dto/ChatRoomDto.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/dto/ChatRoomDto.kt
@@ -93,3 +93,44 @@ data class ExternalCharacterData(
     val age: String,
     val gender: String
 )
+
+/**
+ * 채팅 메시지 전송 요청 DTO
+ */
+data class SendChatMessageRequest(
+    val message: String
+)
+
+/**
+ * 채팅 메시지 전송 응답 DTO (캐릭터 메시지 리스트)
+ */
+data class SendChatMessageResponse(
+    val characterMessages: List<ChatMessageItemDto>
+)
+
+/**
+ * 외부 API 채팅 전송 응답 DTO
+ */
+data class ExternalChatSendResponse(
+    val success: Boolean,
+    val message: String?,
+    val data: ExternalChatSendData?
+)
+
+/**
+ * 외부 API 채팅 전송 데이터 DTO
+ */
+data class ExternalChatSendData(
+    val sessionId: String,
+    val characterResponse: ExternalCharacterMessage
+)
+
+/**
+ * 외부 API 캐릭터 메시지 DTO
+ */
+data class ExternalCharacterMessage(
+    val id: String,
+    val content: String,
+    val timestamp: String,
+    val messageType: String
+)
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/repository/CharacterChatParticipantRepository.kt b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/repository/CharacterChatParticipantRepository.kt
index edd5e60..3d4f144 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/repository/CharacterChatParticipantRepository.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/repository/CharacterChatParticipantRepository.kt
@@ -18,6 +18,14 @@ interface CharacterChatParticipantRepository : JpaRepository<CharacterChatPartic
         member: Member
     ): CharacterChatParticipant?
 
+    /**
+     * 특정 채팅방에 특정 타입(CHARACTER/USER)으로 활성 상태인 참여자 찾기
+     */
+    fun findByChatRoomAndParticipantTypeAndIsActiveTrue(
+        chatRoom: CharacterChatRoom,
+        participantType: ParticipantType
+    ): CharacterChatParticipant?
+
     /**
      * 특정 채팅방의 활성 USER 참여자 수
      */
diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/service/ChatRoomService.kt b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/service/ChatRoomService.kt
index 2a7878c..67d274f 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/service/ChatRoomService.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/chat/room/service/ChatRoomService.kt
@@ -2,6 +2,7 @@ package kr.co.vividnext.sodalive.chat.room.service
 
 import com.fasterxml.jackson.databind.ObjectMapper
 import kr.co.vividnext.sodalive.chat.character.service.ChatCharacterService
+import kr.co.vividnext.sodalive.chat.room.CharacterChatMessage
 import kr.co.vividnext.sodalive.chat.room.CharacterChatParticipant
 import kr.co.vividnext.sodalive.chat.room.CharacterChatRoom
 import kr.co.vividnext.sodalive.chat.room.ParticipantType
@@ -9,8 +10,10 @@ import kr.co.vividnext.sodalive.chat.room.dto.ChatMessageItemDto
 import kr.co.vividnext.sodalive.chat.room.dto.ChatRoomListItemDto
 import kr.co.vividnext.sodalive.chat.room.dto.ChatRoomListQueryDto
 import kr.co.vividnext.sodalive.chat.room.dto.CreateChatRoomResponse
+import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSendResponse
 import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSessionCreateResponse
 import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSessionGetResponse
+import kr.co.vividnext.sodalive.chat.room.dto.SendChatMessageResponse
 import kr.co.vividnext.sodalive.chat.room.repository.CharacterChatMessageRepository
 import kr.co.vividnext.sodalive.chat.room.repository.CharacterChatParticipantRepository
 import kr.co.vividnext.sodalive.chat.room.repository.CharacterChatRoomRepository
@@ -357,4 +360,131 @@ class ChatRoomService(
             )
         }
     }
+
+    @Transactional
+    fun sendMessage(member: Member, chatRoomId: Long, message: String): SendChatMessageResponse {
+        // 1) 방 존재 확인
+        val room = chatRoomRepository.findById(chatRoomId).orElseThrow {
+            SodaException("채팅방을 찾을 수 없습니다.")
+        }
+        // 2) 참여 여부 확인 (USER)
+        val myParticipant = participantRepository.findByChatRoomAndMemberAndIsActiveTrue(room, member)
+            ?: throw SodaException("잘못된 접근입니다")
+        // 3) 캐릭터 참여자 조회
+        val characterParticipant = participantRepository.findByChatRoomAndParticipantTypeAndIsActiveTrue(
+            room,
+            ParticipantType.CHARACTER
+        ) ?: throw SodaException("잘못된 접근입니다")
+
+        val character = characterParticipant.character
+            ?: throw SodaException("오류가 발생했습니다. 다시 시도해 주세요.")
+
+        // 4) 외부 API 호출 준비
+        val userId = generateUserId(member.id!!)
+        val sessionId = room.sessionId
+        val characterUUID = character.characterUUID
+
+        // 5) 외부 API 호출 (최대 3회 재시도)
+        val characterReply = callExternalApiForChatSendWithRetry(userId, characterUUID, message, sessionId)
+
+        // 6) 내 메시지 저장
+        val myMsgEntity = CharacterChatMessage(
+            message = message,
+            chatRoom = room,
+            participant = myParticipant,
+            isActive = true
+        )
+        messageRepository.save(myMsgEntity)
+
+        // 7) 캐릭터 메시지 저장
+        val characterMsgEntity = CharacterChatMessage(
+            message = characterReply,
+            chatRoom = room,
+            participant = characterParticipant,
+            isActive = true
+        )
+        val savedCharacterMsg = messageRepository.save(characterMsgEntity)
+
+        // 8) 응답 DTO 구성 (캐릭터 메시지 리스트 반환 - 단일 요소)
+        val profilePath = characterParticipant.character?.imagePath
+        val defaultPath = profilePath ?: "profile/default-profile.png"
+        val imageUrl = "$imageHost/$defaultPath"
+        val dto = ChatMessageItemDto(
+            messageId = savedCharacterMsg.id!!,
+            message = savedCharacterMsg.message,
+            profileImageUrl = imageUrl,
+            mine = false
+        )
+
+        return SendChatMessageResponse(characterMessages = listOf(dto))
+    }
+
+    private fun callExternalApiForChatSendWithRetry(
+        userId: String,
+        characterUUID: String,
+        message: String,
+        sessionId: String
+    ): String {
+        val maxAttempts = 3
+        var attempt = 0
+        while (attempt < maxAttempts) {
+            attempt++
+            try {
+                return callExternalApiForChatSend(userId, characterUUID, message, sessionId)
+            } catch (e: Exception) {
+                log.warn("[chat] 외부 채팅 전송 실패 attempt={}, error={}", attempt, e.message)
+            }
+        }
+        log.error("[chat] 외부 채팅 전송 최종 실패 attempts={}", maxAttempts)
+        throw SodaException("메시지 전송을 실패했습니다.")
+    }
+
+    private fun callExternalApiForChatSend(
+        userId: String,
+        characterUUID: String,
+        message: String,
+        sessionId: String
+    ): String {
+        val factory = SimpleClientHttpRequestFactory()
+        factory.setConnectTimeout(20000)
+        factory.setReadTimeout(20000)
+
+        val restTemplate = RestTemplate(factory)
+
+        val headers = HttpHeaders()
+        headers.set("x-api-key", apiKey)
+        headers.contentType = MediaType.APPLICATION_JSON
+
+        val requestBody = mapOf(
+            "userId" to userId,
+            "characterId" to characterUUID,
+            "message" to message,
+            "sessionId" to sessionId
+        )
+
+        val httpEntity = HttpEntity(requestBody, headers)
+
+        val response = restTemplate.exchange(
+            "$apiUrl/api/chat",
+            HttpMethod.POST,
+            httpEntity,
+            String::class.java
+        )
+
+        val objectMapper = ObjectMapper()
+        val apiResponse = objectMapper.readValue(
+            response.body,
+            ExternalChatSendResponse::class.java
+        )
+
+        if (!apiResponse.success) {
+            throw SodaException(apiResponse.message ?: "메시지 전송을 실패했습니다.")
+        }
+        val data = apiResponse.data ?: throw SodaException("메시지 전송을 실패했습니다.")
+        val characterContent = data.characterResponse.content
+        if (characterContent.isBlank()) {
+            throw SodaException("메시지 전송을 실패했습니다.")
+        }
+        return characterContent
+    }
 }