diff --git a/src/main.py b/src/main.py
index ca7c11e..f8ecf89 100644
--- a/src/main.py
+++ b/src/main.py
@@ -113,10 +113,13 @@ def _determine_order_quantity(
     total_cash: float,
     candidate: ScanCandidate | None,
     settings: Settings | None,
+    open_position: dict[str, Any] | None = None,
 ) -> int:
     """Determine order quantity using volatility-aware position sizing."""
-    if action != "BUY":
-        return 1
+    if action == "SELL":
+        if open_position is None:
+            return 0
+        return int(open_position.get("quantity") or 0)
     if current_price <= 0 or total_cash <= 0:
         return 0
 
@@ -466,12 +469,18 @@ async def trading_cycle(
     trade_price = current_price
     trade_pnl = 0.0
     if decision.action in ("BUY", "SELL"):
+        sell_position = (
+            get_open_position(db_conn, stock_code, market.code)
+            if decision.action == "SELL"
+            else None
+        )
         quantity = _determine_order_quantity(
             action=decision.action,
             current_price=current_price,
             total_cash=total_cash,
             candidate=candidate,
             settings=settings,
+            open_position=sell_position,
         )
         if quantity <= 0:
             logger.info(
@@ -891,12 +900,18 @@ async def run_daily_session(
             trade_pnl = 0.0
             order_succeeded = True
             if decision.action in ("BUY", "SELL"):
+                daily_sell_position = (
+                    get_open_position(db_conn, stock_code, market.code)
+                    if decision.action == "SELL"
+                    else None
+                )
                 quantity = _determine_order_quantity(
                     action=decision.action,
                     current_price=stock_data["current_price"],
                     total_cash=total_cash,
                     candidate=candidate_map.get(stock_code),
                     settings=settings,
+                    open_position=daily_sell_position,
                 )
                 if quantity <= 0:
                     logger.info(
diff --git a/tests/test_main.py b/tests/test_main.py
index 7f4518a..cd42d38 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -14,6 +14,7 @@ from src.evolution.scorecard import DailyScorecard
 from src.logging.decision_logger import DecisionLogger
 from src.main import (
     _apply_dashboard_flag,
+    _determine_order_quantity,
     _handle_market_close,
     _run_context_scheduler,
     _run_evolution_loop,
@@ -68,6 +69,90 @@ def _make_sell_match(stock_code: str = "005930") -> ScenarioMatch:
     )
 
 
+class TestDetermineOrderQuantity:
+    """Test _determine_order_quantity() helper function."""
+
+    def test_sell_returns_position_quantity(self) -> None:
+        """SELL action should return actual held quantity from open_position."""
+        open_pos = {"decision_id": "abc", "price": 100.0, "quantity": 7}
+        result = _determine_order_quantity(
+            action="SELL",
+            current_price=105.0,
+            total_cash=50000.0,
+            candidate=None,
+            settings=None,
+            open_position=open_pos,
+        )
+        assert result == 7
+
+    def test_sell_without_position_returns_zero(self) -> None:
+        """SELL with no open_position should return 0 (no shares to sell)."""
+        result = _determine_order_quantity(
+            action="SELL",
+            current_price=105.0,
+            total_cash=50000.0,
+            candidate=None,
+            settings=None,
+            open_position=None,
+        )
+        assert result == 0
+
+    def test_sell_with_zero_quantity_returns_zero(self) -> None:
+        """SELL with position quantity=0 should return 0."""
+        open_pos = {"decision_id": "abc", "price": 100.0, "quantity": 0}
+        result = _determine_order_quantity(
+            action="SELL",
+            current_price=105.0,
+            total_cash=50000.0,
+            candidate=None,
+            settings=None,
+            open_position=open_pos,
+        )
+        assert result == 0
+
+    def test_buy_without_position_sizing_returns_one(self) -> None:
+        """BUY with no settings should return 1 (default)."""
+        result = _determine_order_quantity(
+            action="BUY",
+            current_price=50000.0,
+            total_cash=1000000.0,
+            candidate=None,
+            settings=None,
+        )
+        assert result == 1
+
+    def test_buy_with_zero_cash_returns_zero(self) -> None:
+        """BUY with no cash should return 0."""
+        result = _determine_order_quantity(
+            action="BUY",
+            current_price=50000.0,
+            total_cash=0.0,
+            candidate=None,
+            settings=None,
+        )
+        assert result == 0
+
+    def test_buy_with_position_sizing_calculates_correctly(self) -> None:
+        """BUY with position sizing should calculate quantity from budget."""
+        settings = MagicMock(spec=Settings)
+        settings.POSITION_SIZING_ENABLED = True
+        settings.POSITION_VOLATILITY_TARGET_SCORE = 50.0
+        settings.POSITION_BASE_ALLOCATION_PCT = 10.0
+        settings.POSITION_MAX_ALLOCATION_PCT = 30.0
+        settings.POSITION_MIN_ALLOCATION_PCT = 1.0
+
+        # total_cash=1,000,000 * 10% = 100,000 budget
+        # 100,000 // 50,000 = 2 shares
+        result = _determine_order_quantity(
+            action="BUY",
+            current_price=50000.0,
+            total_cash=1000000.0,
+            candidate=None,
+            settings=settings,
+        )
+        assert result == 2
+
+
 class TestSafeFloat:
     """Test safe_float() helper function."""
 
@@ -1396,6 +1481,108 @@ async def test_hold_overridden_to_sell_when_stop_loss_triggered() -> None:
     assert broker.send_order.call_args.kwargs["order_type"] == "SELL"
 
 
+@pytest.mark.asyncio
+async def test_sell_order_uses_actual_held_quantity() -> None:
+    """SELL order should use the actual quantity held, not hardcoded 1."""
+    db_conn = init_db(":memory:")
+    decision_logger = DecisionLogger(db_conn)
+
+    buy_decision_id = decision_logger.log_decision(
+        stock_code="005930",
+        market="KR",
+        exchange_code="KRX",
+        action="BUY",
+        confidence=90,
+        rationale="entry",
+        context_snapshot={},
+        input_data={},
+    )
+    # Bought 5 shares at 100.0
+    log_trade(
+        conn=db_conn,
+        stock_code="005930",
+        action="BUY",
+        confidence=90,
+        rationale="entry",
+        quantity=5,
+        price=100.0,
+        market="KR",
+        exchange_code="KRX",
+        decision_id=buy_decision_id,
+    )
+
+    broker = MagicMock()
+    broker.get_current_price = AsyncMock(return_value=(95.0, -5.0, 0.0))
+    broker.get_balance = AsyncMock(
+        return_value={
+            "output2": [
+                {
+                    "tot_evlu_amt": "100000",
+                    "dnca_tot_amt": "10000",
+                    "pchs_amt_smtl_amt": "90000",
+                }
+            ]
+        }
+    )
+    broker.send_order = AsyncMock(return_value={"msg1": "OK"})
+
+    scenario = StockScenario(
+        condition=StockCondition(rsi_below=30),
+        action=ScenarioAction.BUY,
+        confidence=88,
+        stop_loss_pct=-2.0,
+        rationale="stop loss policy",
+    )
+    playbook = DayPlaybook(
+        date=date(2026, 2, 8),
+        market="KR",
+        stock_playbooks=[
+            {"stock_code": "005930", "stock_name": "Samsung", "scenarios": [scenario]}
+        ],
+    )
+    engine = MagicMock(spec=ScenarioEngine)
+    engine.evaluate = MagicMock(return_value=_make_hold_match())
+
+    market = MagicMock()
+    market.name = "Korea"
+    market.code = "KR"
+    market.exchange_code = "KRX"
+    market.is_domestic = True
+
+    telegram = MagicMock()
+    telegram.notify_trade_execution = AsyncMock()
+    telegram.notify_fat_finger = AsyncMock()
+    telegram.notify_circuit_breaker = AsyncMock()
+    telegram.notify_scenario_matched = AsyncMock()
+
+    await trading_cycle(
+        broker=broker,
+        overseas_broker=MagicMock(),
+        scenario_engine=engine,
+        playbook=playbook,
+        risk=MagicMock(),
+        db_conn=db_conn,
+        decision_logger=decision_logger,
+        context_store=MagicMock(
+            get_latest_timeframe=MagicMock(return_value=None),
+            set_context=MagicMock(),
+        ),
+        criticality_assessor=MagicMock(
+            assess_market_conditions=MagicMock(return_value=MagicMock(value="NORMAL")),
+            get_timeout=MagicMock(return_value=5.0),
+        ),
+        telegram=telegram,
+        market=market,
+        stock_code="005930",
+        scan_candidates={},
+    )
+
+    broker.send_order.assert_called_once()
+    call_kwargs = broker.send_order.call_args.kwargs
+    assert call_kwargs["order_type"] == "SELL"
+    assert call_kwargs["quantity"] == 5  # actual held quantity, not 1
+
+
 @pytest.mark.asyncio
 async def test_handle_market_close_runs_daily_review_flow() -> None:
     """Market close should aggregate, create scorecard, lessons, and notify."""