An exemplary prism sheet includes a transparent main body. The main body includes a first surface, a second surface opposite to the first surface, a plurality of spherical depressions formed in the first surface, and a plurality of triangular pyramidal depressions and hexagonal pyramidal depressions formed in the second surface. Each of the triangular pyramidal depressions is surrounded by three adjacent hexagonal pyramidal depressions. A backlight module using the present prism sheet is also provided.