A backlight module including a diffuser, a reflector, a side light source, a prism lens and a TIR (total internal reflection) lens is disclosed. The reflector is disposed under the diffuser. The side light source is disposed on a side between the diffuser and the reflector. The prism lens is disposed between the side light source and the reflector. The TIR lens is disposed on a bottom of the diffuser and adjacent to the side light source.