The present invention provides a backlight module, which comprises a waveguide has an incident surface and light-emitting surface. A light source is arranged on a side of the incident surface. An optical module is arranged above the waveguide and facing the light-emitting surface. The optical module includes a least one optical film having a crease at one side thereof. At least a positioning arrangement is arranged on a side surface of the waveguide other than the incident surface. A space is defined between the positioning arrangement and the side surface of the waveguide. The crease of the optical film is received within the space. The present invention further provides a liquid crystal display module incorporated with a backlight module disclosed. Accordingly, when the optical films is experiencing an expansion or contraction resulted from temperature gradient, the robust can always make the optical films properly seated within the receiving space defined by the positioning arrangement and the waveguide. As a result, the optical films can be effectively prevented from being deformed or creating a wave-form deformation.