diff --git a/packages/bot/src/lib/logger.ts b/packages/bot/src/lib/logger.ts
index 15edeb2..1543ad5 100644
--- a/packages/bot/src/lib/logger.ts
+++ b/packages/bot/src/lib/logger.ts
@@ -27,6 +27,11 @@ const logger = pino({
   formatters: {
     level: (label) => ({ level: label }),
   },
+  // Serialize Error objects properly (pino defaults to {} for non-'err' keys)
+  serializers: {
+    error: pino.stdSerializers.err,
+    err: pino.stdSerializers.err,
+  },
   // ISO 8601 timestamp with timezone offset
   timestamp: pino.stdTimeFunctions.isoTime,
   // Development: pretty print
diff --git a/packages/bot/src/schedulers/rss-poller.ts b/packages/bot/src/schedulers/rss-poller.ts
index e816688..b0afe1e 100644
--- a/packages/bot/src/schedulers/rss-poller.ts
+++ b/packages/bot/src/schedulers/rss-poller.ts
@@ -5,6 +5,7 @@
  */
 
 import { getMemberService } from '../services/member.service';
+import { getPostService } from '../services/post.service';
 import { getRssService, type PollResult, type RssFeedItem } from '../services/rss.service';
 import { type Member, MemberStatus } from '@blog-study/shared/db';
 import logger from '../lib/logger';
@@ -79,26 +80,36 @@ export class RssPoller {
 
     try {
       const rssService = getRssService();
+      const postService = getPostService();
       const items = await rssService.fetchFeed(member.rssUrl);
-      
+
+      if (items.length === 0) {
+        return { memberId: member.id, success: true, newItems: [] };
+      }
+
+      // Batch duplicate check: 1 IN query instead of N individual SELECTs
+      // postService.create() has its own getByUrl guard as a write-time safety net
+      const feedUrls = items.map(item => item.link).filter(Boolean);
+      const existingUrls = await postService.getExistingUrls(feedUrls);
+      const newItems = items.filter(item => !existingUrls.has(item.link));
+
       return {
         memberId: member.id,
         success: true,
-        newItems: items,
+        newItems,
       };
     } catch (error) {
       // Requirements: 6.5 - Log error and continue processing other feeds
-      const errorMessage = error instanceof Error ? error.message : String(error);
       logger.error({
         member: member.discordUsername,
-        error: errorMessage,
+        error,
       }, '📡 [RSS] 멤버 피드 폴링 에러');
-      
+
       return {
         memberId: member.id,
         success: false,
         newItems: [],
-        error: errorMessage,
+        error: error instanceof Error ? error.message : String(error),
       };
     }
   }
@@ -141,13 +152,13 @@ export class RssPoller {
           try {
             await this.onNewPost(member, result.newItems);
           } catch (callbackError) {
-            const errorMsg = callbackError instanceof Error
-              ? callbackError.message
-              : String(callbackError);
             logger.error({
               member: member.discordUsername,
-              error: errorMsg,
+              error: callbackError,
             }, '📡 [RSS] 콜백 에러');
+            const errorMsg = callbackError instanceof Error
+              ? callbackError.message
+              : String(callbackError);
             errors.push(`Callback error for ${member.discordUsername}: ${errorMsg}`);
           }
         }
diff --git a/packages/bot/src/services/post.service.ts b/packages/bot/src/services/post.service.ts
index e0503c2..8903cdd 100644
--- a/packages/bot/src/services/post.service.ts
+++ b/packages/bot/src/services/post.service.ts
@@ -4,7 +4,7 @@
  * Requirements: 6.3, 6.4, 6.6
  */
 
-import { eq, and, count } from 'drizzle-orm';
+import { eq, and, count, inArray } from 'drizzle-orm';
 import {
   getDb,
   posts,
@@ -175,6 +175,22 @@ export class PostService {
     return post || null;
   }
 
+  /**
+   * Get existing URLs from a list of URLs (batch duplicate check)
+   * Note: URL is globally unique across all members (schema unique constraint),
+   * so no memberId scoping is needed here.
+   */
+  async getExistingUrls(urls: string[]): Promise<Set<string>> {
+    if (urls.length === 0) return new Set();
+
+    const results = await this.db
+      .select({ url: posts.url })
+      .from(posts)
+      .where(inArray(posts.url, urls));
+
+    return new Set(results.map(r => r.url));
+  }
+
   /**
    * Get all posts
    */