A backlight module. The backlight module includes a first light guide, a second light guide, and a plurality of light sources. The second light guide comprises a least one first medium transmissive and a least one second transmissive medium. The transmissive media are disposed between the incident surface and the emergent surface and have different refractive indices. Light emitted from the light sources enters the second light guide through an incident surface of the second light guide and exits the second light guide through an emergent surface thereof. Light emitted from the second light guide enters the first light guide through a first side surface thereof.