The present invention provides a backlight module which comprises a waveguide, an optical film, an elastic frame, and dowel pins. Wherein at least corners of the optical film is securely attached to the elastic frame, and wherein the dowel pints are attached to the elastic frame, and the optical film is disposed on top of the waveguide. Wherein corners of the optical film are provided with openings with which the optical films are readily positioned with respect to the waveguide by extending the dowel pins through the openings. And wherein the strength of the dowel pins is stronger than the strength of the elastic frame. The present invention further provides a liquid crystal display device incorporated with the backlight module disclosed above. By this arrangement, once the positioning of the optical films can he ensured, the optical quality of the backlight module can also be ensured.