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, a backlight source (6) arranged in the backplane, and a plurality of mounting member (8) in the backplane to position and fix the light guide plate (4). The light guide plate (4) includes a main body (42) and a plurality of mounting sections (44) extending outwards from sides of the main body. Each of the mounting sections (44) includes a first lug (442) and a second lug (444) that are spaced from each other. The mounting members (8) each include a base (82) and first, second, and third positioning pillars (84, 86, 88) extending upwards from the base (82) and arranged sequentially to space from each other. The main body (42) is positioned against the base (82) and the second positioning pillar (86). The first lug (442) is positioned against the base (82) and the first positioning pillar (84). The second lug (444) is positioned against the base (82) and the third positioning pillar (88).