The present invention provides a backlight module and a liquid crystal display device using the backlight module. The backlight module includes a backplane (2), a light guide plate (4) arranged in the backplane (2), a backlight source (6) arranged in the backplane (2) at one side of the light guide plate (4), a light shielding film (8) mounted on the light guide plate (4) and the backplane (2) and located above the backlight source (6), and an optic film assembly (10) arranged on the light shielding film (8) and the light guide plate (4). The light shielding film (8) has an end fixedly connected to an upper surface of the light guide plate (4) and an opposite end fixedly connected to the backplane (2). The present invention provides an arrangement of a light shielding film above the backlight source to effectively prevent light leaking and enhance the optic quality of the backlight module. Further, a light shielding section of the light shielding film is arranged to be extendable so as to effectively prevent shifting of the light shielding film resulting from an external force acting thereon during the transportation thereof thereby further effectively preventing the occurrence of light leaking and being helpful for bezel slimming of the liquid crystal display device.