A light source module includes a light guide plate, a first inverse prism sheet, a second inverse prism sheet, and a light source. The light guide plate has a light incident surface, a first light emitting surface and an opposing second light emitting surface. The second light emitting surface has a plurality of microstructures. Each microstructure is a recessed structure. The first inverse prism sheet is disposed beside the first light emitting surface of the light guide plate. The first inverse prism sheet includes a plurality of first prism columns. The first prism columns face the first light emitting surface. The second inverse prism sheet is disposed beside the second light emitting surface of the light guide plate. The second inverse prism sheet includes a plurality of second prism columns. The second prism columns face the second light emitting surface. The light source is disposed beside the light incident surface.