I tried removing WS_EX_APPWINDOW but it didn't work. In fact, I've used that technique in MFC and it works fine. I also written a fuction to modify window style and it works fine with normal style (e.g WS_SYSMENU, WS_THICKFRAME,..) but WS_EX_APPwindow. Any suggestion? Func ModifyWindowStyle( $style, $action = True, $isExStyle = False, $windowHandle = @GUI_WinHandle ) Const $NORMAL_STYLE = 0 Const $EXTENDED_STYLE = 1 ; Get current window style $currentStyle = GUIGetStyle( $windowHand