diff --git a/backend/src/main/java/com/petshop/backend/controller/AiChatController.java b/backend/src/main/java/com/petshop/backend/controller/AiChatController.java
index 34de297c..ba08b418 100644
--- a/backend/src/main/java/com/petshop/backend/controller/AiChatController.java
+++ b/backend/src/main/java/com/petshop/backend/controller/AiChatController.java
@@ -8,6 +8,7 @@ import com.petshop.backend.repository.PetRepository;
 import com.petshop.backend.repository.UserRepository;
 import com.petshop.backend.service.OpenRouterService;
 import com.petshop.backend.util.AuthenticationHelper;
+import com.petshop.backend.util.ContentFilter;
 import jakarta.validation.Valid;
 import org.springframework.http.ResponseEntity;
 import org.springframework.security.access.prepost.PreAuthorize;
@@ -49,6 +50,7 @@ public class AiChatController {
         if (request.getMessage() == null || request.getMessage().isBlank()) {
             return ResponseEntity.badRequest().body(AiChatResponse.fail("Message cannot be empty"));
         }
+        ContentFilter.validate(request.getMessage());
 
         User user = getCurrentUser();
 
diff --git a/backend/src/main/java/com/petshop/backend/service/ChatService.java b/backend/src/main/java/com/petshop/backend/service/ChatService.java
index 97cd584a..0e80fc1a 100644
--- a/backend/src/main/java/com/petshop/backend/service/ChatService.java
+++ b/backend/src/main/java/com/petshop/backend/service/ChatService.java
@@ -9,6 +9,7 @@ import com.petshop.backend.entity.Conversation;
 import com.petshop.backend.entity.Message;
 import com.petshop.backend.entity.User;
 import com.petshop.backend.exception.ResourceNotFoundException;
+import com.petshop.backend.util.ContentFilter;
 import com.petshop.backend.repository.ConversationRepository;
 import com.petshop.backend.repository.MessageRepository;
 import com.petshop.backend.repository.UserRepository;
@@ -138,6 +139,8 @@ public class ChatService {
             }
         }
 
+        ContentFilter.validate(request.getContent());
+
         Message message = new Message();
         message.setConversationId(conversationId);
         message.setSenderId(userId);
diff --git a/backend/src/main/java/com/petshop/backend/util/ContentFilter.java b/backend/src/main/java/com/petshop/backend/util/ContentFilter.java
new file mode 100644
index 00000000..0552b2d2
--- /dev/null
+++ b/backend/src/main/java/com/petshop/backend/util/ContentFilter.java
@@ -0,0 +1,30 @@
+package com.petshop.backend.util;
+
+import com.petshop.backend.exception.BusinessException;
+
+import java.util.Locale;
+import java.util.Set;
+import java.util.regex.Pattern;
+
+public class ContentFilter {
+
+    private static final Pattern SCRIPT_PATTERN = Pattern.compile(
+            "<script|javascript:|on\\w+\\s*=", Pattern.CASE_INSENSITIVE);
+
+    private static final Set<String> PROFANITY = Set.of(
+            "profanityOne", "profanityTwo", "profanityThree"
+    );
+
+    public static void validate(String input) {
+        if (input == null || input.isBlank()) return;
+        if (SCRIPT_PATTERN.matcher(input).find()) {
+            throw new BusinessException("Message contains prohibited content");
+        }
+        String lower = input.toLowerCase(Locale.ROOT);
+        for (String word : PROFANITY) {
+            if (lower.contains(word)) {
+                throw new BusinessException("Message contains prohibited language");
+            }
+        }
+    }
+}