A backlight module includes a front frame, a backboard, and a light source. The front frame and the backboard define opposite outermost surfaces of the backlight module. The backboard includes a frame and a light-shield plate. The frame is coupled with the front frame. The frame has a plurality of plates surroundingly defining an empty part and at least one side wall extending from one of the plates to be coupled with the front frame. Each one of the plates has a first surface, a second surface opposite to the first surface, and at least one rib and/or trough, and the rib and/or trough is disposed on the first surface and is spaced apart from the side wall. The light-shield plate covers the empty part. The light source is disposed between the front frame and the backboard.