diff --git a/trader/okx/trader_account.go b/trader/okx/trader_account.go
index 53fa0550..416a109d 100644
--- a/trader/okx/trader_account.go
+++ b/trader/okx/trader_account.go
@@ -82,31 +82,14 @@ func (t *OKXTrader) GetBalance() (map[string]interface{}, error) {
 
 // SetMarginMode sets margin mode
 func (t *OKXTrader) SetMarginMode(symbol string, isCrossMargin bool) error {
-	instId := t.convertSymbol(symbol)
 	t.isCrossMargin = isCrossMargin
 	mgnMode := t.marginMode()
 
-	body := map[string]interface{}{
-		"instId":  instId,
-		"mgnMode": mgnMode,
-	}
-
-	_, err := t.doRequest("POST", "/api/v5/account/set-isolated-mode", body)
-	if err != nil {
-		// Ignore error if already in target mode
-		if strings.Contains(err.Error(), "already") {
-			logger.Infof("  ✓ %s margin mode is already %s", symbol, mgnMode)
-			return nil
-		}
-		// Cannot change when there are positions
-		if strings.Contains(err.Error(), "position") {
-			logger.Infof("  ⚠️ %s has positions, cannot change margin mode", symbol)
-			return nil
-		}
-		return err
-	}
-
-	logger.Infof("  ✓ %s margin mode set to %s", symbol, mgnMode)
+	// OKX V5 unified account applies cross/isolated per order via tdMode,
+	// while leverage uses mgnMode on /account/set-leverage.
+	// Persist the configured mode locally so subsequent leverage/order calls use it,
+	// instead of calling the legacy isolated-mode endpoint that returns 51000 errors.
+	logger.Infof("  ✓ %s margin mode configured as %s (applied via tdMode/mgnMode on subsequent requests)", symbol, mgnMode)
 	return nil
 }
 
diff --git a/trader/okx/trader_margin_mode_test.go b/trader/okx/trader_margin_mode_test.go
index b0a78305..b633a364 100644
--- a/trader/okx/trader_margin_mode_test.go
+++ b/trader/okx/trader_margin_mode_test.go
@@ -98,6 +98,34 @@ func TestOKXSetLeverageUsesConfiguredMarginMode(t *testing.T) {
 	}
 }
 
+func TestOKXSetMarginModeUpdatesFutureRequestsWithoutAPIError(t *testing.T) {
+	rt := &recordingTransport{}
+	trader := newTestOKXTrader(rt, true)
+
+	if err := trader.SetMarginMode("BTCUSDT", false); err != nil {
+		t.Fatalf("SetMarginMode failed: %v", err)
+	}
+
+	if len(rt.requestsForPath("/api/v5/account/set-isolated-mode")) != 0 {
+		t.Fatal("expected SetMarginMode not to call legacy isolated-mode endpoint")
+	}
+
+	if err := trader.SetLeverage("BTCUSDT", 5); err != nil {
+		t.Fatalf("SetLeverage failed: %v", err)
+	}
+
+	leverageRequests := rt.requestsForPath(okxLeveragePath)
+	if len(leverageRequests) != 2 {
+		t.Fatalf("expected 2 leverage requests, got %d", len(leverageRequests))
+	}
+
+	for _, req := range leverageRequests {
+		if req.Body["mgnMode"] != "isolated" {
+			t.Fatalf("expected isolated leverage mode after SetMarginMode(false), got %#v", req.Body["mgnMode"])
+		}
+	}
+}
+
 func TestOKXOpenLongUsesConfiguredMarginMode(t *testing.T) {
 	rt := &recordingTransport{}
 	trader := newTestOKXTrader(rt, false)