A backlight module including a frame, a plurality of light guide plates, a plurality of high refractive mediums, and a plurality of light sources is provided. The light guide plates are disposed within the frame and each of the light guide plates has at least one light incident surface and at least one light emitting surface. Additionally, high refractive mediums are disposed between two neighboring light guide plates. Moreover, the light sources are disposed beside the light incident surfaces of the light guide plates.