A backlight module includes a light source unit, an optical fiber, a diverging lens and a light guide unit. The light source unit includes a first light source emitting red light, a second light source emitting green light and a third light source emitting blue light. The optical fiber includes a first, second, and third incident branches and a light output portion. The three incident branches converge into the light output portion and are aligned with the three light sources to guide and mix red, blue, and green light to form white light. The diverging lens is aligned with the light output portion to receive and diverge the white light. The light guide unit faces the diverging lens to receive the white light.