A backlight module includes a light source and a light guide plate. The light guide plate includes a light-receiving surface next to a light source, a light-emitting surface, and a light-reflecting surface oppose to the light-emitting surface. A plurality of notches are formed on the light-reflecting surface, and each notch has a first inner surface facing the light source and a second inner surface back to the light source and opposite to the first inner surface. The inclination angle of the first inner surface with respect to the light-reflecting surface is no more than 35 degrees.