I found this function: Func WinGetTrans($sTitle, $sText = "") Local $hWnd = WinGetHandle($sTitle, $sText) If Not $hWnd Then Return -1 Local $aRet = DllCall("user32.dll", "int", "GetLayeredWindowAttributes", "hwnd", $hWnd, "ptr", 0, "int_ptr", 0, "ptr", 0) If @error Or Not $aRet[0] Then Return -1 Return $aRet[3] EndFunc and used it: $wgt = WinGetTitle("") WinSetTrans($wgt,"",100) MsgBox(0,"",WinGetTrans($wgt)) WinSetTrans($wgt,"",255) Func WinGetTrans($sTitle, $sText =