A backlight module includes a light source and a light guide plate. The light guide plate includes a base plate and a reflecting film. The base plate has an upper surface on which a plurality of protrusions is formed, a curved bottom surface opposite to the upper surface, and a housing defined therein. The light source is accommodated in the housing. The reflecting film is plated on the curved bottom surface, for reflecting the light beams reaching the curved bottom surface to emit from the upper surface. The plurality of protrusions diffuses light beams.