diff --git a/src/ui/flutter/lib/mill/position.dart b/src/ui/flutter/lib/mill/position.dart
index 50d14f6f..c7fa23d9 100644
--- a/src/ui/flutter/lib/mill/position.dart
+++ b/src/ui/flutter/lib/mill/position.dart
@@ -264,7 +264,7 @@ class Position {
     // step counter
     //ss += '${recorder?.halfMove ?? 0} ${recorder?.fullMove ?? 0}';
 
-    print("fen = " + ss);
+    //print("fen = " + ss);
 
     return ss;
   }
@@ -306,7 +306,7 @@ class Position {
   */
     bool ret = false;
 
-    print("position: command = $move");
+    //print("doMove $move");
 
     if (move.length > "Player".length &&
         move.substring(0, "Player".length - 1) == "Player") {
@@ -578,7 +578,7 @@ class Position {
 
         // not in moveTable
         if (md == moveDirectionNumber) {
-          print("putPiece: [$s] is not in [$currentSquare]'s moveTable");
+          print("putPiece: [$s] is not in [$currentSquare]'s move table.");
           return false;
         }
       }
@@ -742,7 +742,7 @@ class Position {
   }
 
   bool checkGameOverCondition() {
-    print("Checking game over condition ...");
+    //print("Is game over?");
 
     if (phase == Phase.ready || phase == Phase.gameOver) {
       return true;
@@ -752,7 +752,7 @@ class Position {
       winner = Color.draw;
       phase = Phase.gameOver;
       gameOverReason = GameOverReason.drawReasonRule50;
-      print("Game over, draw, because of $gameOverReason");
+      print("Game over, draw, because of $gameOverReason.");
       return true;
     }
 
@@ -768,7 +768,7 @@ class Position {
     }
 
     bool isNoWay = isAllSurrounded();
-    print("phase = $phase, action = $action, isAllSurrounded = $isNoWay");
+    //print("phase = $phase, action = $action, isAllSurrounded = $isNoWay");
     if (phase == Phase.moving && action == Act.select && isNoWay) {
       if (rule.isLoseButNotChangeSideWhenNoWay) {
         setGameOver(
@@ -776,12 +776,12 @@ class Position {
         return true;
       } else {
         changeSideToMove(); // TODO: Need?
-        print("Game is not over");
+        //print("Game is not over");
         return false;
       }
     }
 
-    print("Game is NOT over");
+    //print("Game is NOT over");
     return false;
   }
 
@@ -1417,14 +1417,14 @@ class Position {
     // Full
     if (pieceCountOnBoard[Color.black] + pieceCountOnBoard[Color.white] >=
         rankNumber * fileNumber) {
-      print("Board is full.");
+      //print("Board is full.");
       return true;
     }
 
     // Can fly
     if (pieceCountOnBoard[sideToMove()] <= rule.nPiecesAtLeast &&
         rule.allowFlyWhenRemainThreePieces) {
-      print("Can fly.");
+      //print("Can fly.");
       return false;
     }
 
@@ -1443,7 +1443,7 @@ class Position {
       }
     }
 
-    print("No way.");
+    //print("No way.");
     return true;
   }
 
@@ -1500,7 +1500,7 @@ class Position {
     String moves = "";
     int posAfterLastRemove = 0;
 
-    print("recorder.movesCount = ${recorder.movesCount}");
+    //print("recorder.movesCount = ${recorder.movesCount}");
 
     for (i = recorder.movesCount - 1; i >= 0; i--) {
       //if (recorder.moveAt(i).type == MoveType.remove) break;
@@ -1511,17 +1511,17 @@ class Position {
       posAfterLastRemove = i + 1;
     }
 
-    print("[movesSinceLastRemove] posAfterLastRemove = $posAfterLastRemove");
+    //print("[movesSinceLastRemove] posAfterLastRemove = $posAfterLastRemove");
 
     for (int i = posAfterLastRemove; i < recorder.movesCount; i++) {
       moves += " ${recorder.moveAt(i).move}";
     }
 
-    print("moves = $moves");
+    //print("moves = $moves");
 
     var idx = moves.indexOf('-(');
     if (idx != -1) {
-      print("moves[$idx] is -(");
+      //print("moves[$idx] is -(");
       assert(false);
     }
 
@@ -1535,7 +1535,7 @@ class Position {
   void changeSideToMove() {
     them = _sideToMove;
     _sideToMove = Color.opponent(_sideToMove);
-    print("Change sideToMove to $_sideToMove");
+    print("$_sideToMove to move.");
   }
 
   get halfMove => recorder.halfMove;
diff --git a/src/ui/flutter/lib/painting/pieces_painter.dart b/src/ui/flutter/lib/painting/pieces_painter.dart
index 25568570..fe72e76d 100644
--- a/src/ui/flutter/lib/painting/pieces_painter.dart
+++ b/src/ui/flutter/lib/painting/pieces_painter.dart
@@ -138,7 +138,7 @@ class PiecesPainter extends PiecesBasePainter {
           canvas.drawCircle(pps.pos, pieceInnerRadius, paint);
           break;
         case Piece.ban:
-          print("pps.piece is Ban");
+          //print("pps.piece is Ban");
           break;
         default:
           assert(false);
diff --git a/src/ui/flutter/lib/widgets/board.dart b/src/ui/flutter/lib/widgets/board.dart
index 7ac20546..d22a8e5a 100644
--- a/src/ui/flutter/lib/widgets/board.dart
+++ b/src/ui/flutter/lib/widgets/board.dart
@@ -80,13 +80,13 @@ class Board extends StatelessWidget {
 
         final column = (dx - padding) ~/ squareWidth;
         if (column < 0 || column > 6) {
-          print("Tap on column $column skip");
+          print("Tap on column $column (ignored).");
           return;
         }
 
         final row = (dy - padding - digitsHeight) ~/ squareWidth;
         if (row < 0 || row > 6) {
-          print("Tap on row $row skip");
+          print("Tap on row $row (ignored).");
           return;
         }
 
diff --git a/src/ui/flutter/lib/widgets/game_page.dart b/src/ui/flutter/lib/widgets/game_page.dart
index 95799fbf..736c40c6 100644
--- a/src/ui/flutter/lib/widgets/game_page.dart
+++ b/src/ui/flutter/lib/widgets/game_page.dart
@@ -54,7 +54,7 @@ class _GamePageState extends State<GamePage> {
 
   @override
   void initState() {
-    print("engineType = ${widget.engineType}");
+    print("Engine type: ${widget.engineType}");
 
     Game.shared.setWhoIsAi(widget.engineType);
 
@@ -65,7 +65,7 @@ class _GamePageState extends State<GamePage> {
 
   changeStatus(String status) {
     if (context == null) {
-      print("[changeStatus] context == null, return");
+      //print("[changeStatus] context == null, return");
       return;
     }
 
@@ -74,7 +74,7 @@ class _GamePageState extends State<GamePage> {
 
   void showTips() {
     if (context == null) {
-      print("[showTips] context == null, return");
+      //print("[showTips] context == null, return");
       return;
     }
 
@@ -105,7 +105,7 @@ class _GamePageState extends State<GamePage> {
     int sq = indexToSquare[index];
 
     if (sq == null) {
-      print("putPiece skip index: $index");
+      //print("putPiece skip index: $index");
       return;
     }
 
@@ -251,7 +251,7 @@ class _GamePageState extends State<GamePage> {
       changeStatus(S.of(context).gameStarted);
 
       if (Game.shared.isAiToMove()) {
-        print("New Game: AI's turn.");
+        print("New game, AI to move.");
         engineToGo();
       }
     }