A light guide plate (200) includes an emission surface (204), a bottom surface (206), and at least one chamfering (202). The emission surface intersects with the chamfering. The bottom surface intersects with the chamfering and is opposite to the emission surface. The light guide plate further includes a plurality of prism structures (208) formed at least one of within and on at least one of the emission surface and the bottom surface. A backlight module (50), adopting the above-mentioned light guide plate, further includes a corresponding light source (220) positioned beside each chamfering of the light guide plate.