An exemplary light guide plate includes a light input surface, a bottom surface, a light output surface opposite to the bottom surface, and a plurality of dots. The dots are arranged on the bottom surface in series of adjacent columns parallel to the light input surface. A distance between two dot centers of two adjacent dots and sizes of the dots in a same dot column are uniform. Each dot column defines a column axis that passes through dot centers of each of the dots. A distance between two adjacent column axes increases with increasing distance from the first light input surface. A backlight module using the light guide plate is provided.