A prism sheet including a transparent substrate, a plurality of prism rods and at least one optical grating structure is provided. The transparent substrate has a first surface and a second surface opposite to the first surface. The prism rods are disposed on the first surface, wherein each of the prism rods extends along a first direction, and the prism rods are arranged along a second direction. The optical grating structure is disposed on the first surface and located between two adjacent ones of the prism rods, wherein the optical grating structure extends along the first direction. In addition, a backlight module using the above-mentioned prism sheet is also provided.