A backlight module and a liquid crystal device are disclosed. The backlight module includes a plastic frame, an aluminum extrusion, and a light guiding plate. The plastic frame and the aluminum extrusion prohibit the light guiding plate from moving in an up and down direction. Wherein the light guiding plate is disposed on the aluminum extrusion. The light guiding plate includes a body, and a first position portion extends along the body towards the aluminum extrusion. The aluminum extrusion includes a position slot corresponding to the first position portion, and the first position portion closely engages with the first position slot. The backlight module and the liquid crystal device fix the light guiding plate by engaging the light guiding plate, the aluminum extrusion, and the plastic frame so that the light guiding plate is stably fixed and the light coupling is stable.