A back light module including a frame, a light-guide plate and a light source is provided. The frame has a opening and a first surface and a second surface opposite to the first surface. The opening is extended from the first surface to the second surface of the frame, so that an inner surface of the opening is connected to the first surface and the second surface. At least a portion of the inner surface is slanted toward the inner of the opening. The light-guide plate is integrated with the frame and at least a portion of the opening is filled with the light-guide plate. The light-guide plate is tightly attached to the inner surface of the frame. The light source is adjacent to the light-guide plate.