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), and a heat dissipation plate (8) arranged between the backlight source (6) and the backplane (2). The backplane (2) includes a bottom plate (22) and a side plate (24) perpendicularly connected to the bottom plate (22). The backlight source (6) includes a PCB (62) and an LED chip (64) mounted on the PCB (62). The PCB (62) is arranged on the bottom plate (22) of the backplane (2) and the heat dissipation plate (8). The PCB (62) includes a mounting section (622) and a lapping section (624) connected to the mounting section (622). The heat dissipation plate (8) includes a support section (82) and a bearing section (84) connected to the support section (82). The lapping section (624) is positioned on and overlaps the bearing section (84). The light guide plate (4) is carried on the support section (82) and the lapping section (624).