diff --git a/backend/app/api/admin.py b/backend/app/api/admin.py
index 2586ea0..4b7f57e 100644
--- a/backend/app/api/admin.py
+++ b/backend/app/api/admin.py
@@ -2,8 +2,9 @@
 Admin API for data collection management.
 """
 from typing import List
+from datetime import datetime
 
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.orm import Session
 from pydantic import BaseModel
 
@@ -24,8 +25,8 @@ class JobLogResponse(BaseModel):
     id: int
     job_name: str
     status: str
-    started_at: str
-    finished_at: str | None
+    started_at: datetime
+    finished_at: datetime | None
     records_count: int | None
     error_msg: str | None
 
@@ -42,7 +43,7 @@ class CollectResponse(BaseModel):
 async def collect_stocks(
     current_user: CurrentUser,
     db: Session = Depends(get_db),
-    biz_day: str = None,
+    biz_day: str = Query(None, regex=r"^\d{8}$", description="Business day in YYYYMMDD format"),
 ):
     """Collect stock master data from KRX."""
     try:
@@ -60,7 +61,7 @@ async def collect_stocks(
 async def collect_sectors(
     current_user: CurrentUser,
     db: Session = Depends(get_db),
-    biz_day: str = None,
+    biz_day: str = Query(None, regex=r"^\d{8}$", description="Business day in YYYYMMDD format"),
 ):
     """Collect sector classification data from WISEindex."""
     try:
@@ -78,8 +79,8 @@ async def collect_sectors(
 async def collect_prices(
     current_user: CurrentUser,
     db: Session = Depends(get_db),
-    start_date: str = None,
-    end_date: str = None,
+    start_date: str = Query(None, regex=r"^\d{8}$", description="Start date in YYYYMMDD format"),
+    end_date: str = Query(None, regex=r"^\d{8}$", description="End date in YYYYMMDD format"),
 ):
     """Collect price data using pykrx."""
     try:
@@ -97,7 +98,7 @@ async def collect_prices(
 async def collect_valuations(
     current_user: CurrentUser,
     db: Session = Depends(get_db),
-    biz_day: str = None,
+    biz_day: str = Query(None, regex=r"^\d{8}$", description="Business day in YYYYMMDD format"),
 ):
     """Collect valuation data from KRX."""
     try:
@@ -115,7 +116,7 @@ async def collect_valuations(
 async def get_collection_status(
     current_user: CurrentUser,
     db: Session = Depends(get_db),
-    limit: int = 20,
+    limit: int = Query(20, gt=0, le=100, description="Number of records to return"),
 ):
     """Get recent job execution status."""
     jobs = (