I try to disable the minimize box in one of my MDI child frame. However, I cannot seem to disable the minimize box. When I created this mdi child frame, the style I used was dwStyle = WS_CHILD | WS_OVERLAPPED | WS_CAPTION |WS_SYSMENU | WS_THICKFRAME | WS_MINIMIZEBOX; I try to get the system menu of this mdi child frame to do the disabling. Nothing seems to work. I need to enable and disable this minimize box depending on certain state.