A backlight module includes a light guide plate, micro-structures, at least one light source, and a first prism sheet. The light guide plate includes a first surface, a second surface, and a light incident surface connecting the first surface and the second surface. The micro-structures are disposed on at least one of the first surface and the second surface. The light source is disposed beside the light incident surface and capable of emitting a light beam. The first prism sheet includes a first transparent substrate and first prism structures. The first surface is located between the second surface and the first transparent substrate. The first transparent substrate is disposed among the first surface and the first prism structures. Each first prism structure has a first vertex angle protruding away from the first transparent substrate, and the first vertex angle falls within a range of 67 degrees to 83 degrees.