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. Each dot column defines a column axis that passes through centers of the dots. A distance between two adjacent column axes increases with increasing distance from the first light input surface. A distance between centers of two adjacent dots in the same column increase with increasing distance from a center of the column to each of two opposite ends of the column. A backlight module using the light guide plate is also provided.