A backlight module includes a substrate, a plurality of LED packages mounted on the substrate and a light diffusion board located above the LED packages. The light diffusion board includes a light incident surface facing toward the LED packages and a light output surface. A plurality of light-guiding portions is configured extending from the incident surface of the light diffusion board toward the LED package. Each light-guiding portion comprises a concave surface at an outer periphery thereof. A diameter of each light-guiding portion decreases gradually from light diffusion board toward the LED packages. The concave surface of each light-guiding portion is recessed inwardly from the outer periphery of the light-guiding portion. Light from the LED packages and emitting into the light-guiding potions is divergently and uniformly adjusted into the light diffusion board by the concave surfaces of the light-guiding portions.