The present invention provides a light guide plate and a backlight module using the light guide plate. The light guide plate has an upper surface forming upper micro-structures and a lower surface forming lower micro-structures. The upper and lower micro-structures are set parallel to propagation direction of the light that emits from a backlight source traveling within the light guide plate. The upper and lower micro-structures each include a plurality of periodically and successively juxtaposed strip-like units. Each of the strip-like units forms a prism. The strip-like units of the upper and lower micro-structures are juxtaposed in the same direction. With the combination and arrangement of the upper micro-structures and lower micro-structures, collimation of light is improved after the light from an LED light source enters the light guide plate so as to improve convergence of the light inside a section.