A backlight module includes a light guide plate (LGP), a light source, and at least one prism sheet. The LGP includes a light emitting surface, a bottom surface, a light incident surface, and a plurality of first microstructures on the bottom surface. Each of the first microstructure is a recessed structure and includes a first surface and a second surface. An included angle between the first surface and the bottom surface ranges from 15 degrees to 27 degrees. An included angle between the second surface and the bottom surface ranges from 50 degrees to 90 degrees. The light source provides a light beam, and an included angle between a light emitting direction of the light beam emitted from the light emitting surface of the LGP and a normal direction of the light emitting surface is greater than 30 degrees. The prism sheet is disposed above the light emitting surface.