A backlight module is applied to a liquid crystal display device. The liquid crystal display device includes an optical film set having at least one optical film. The optical film set is disposed above the backlight module. The backlight module includes a housing and a spacer. The housing has a bottom plate provided with a through opening, an inward side and an outward side, wherein the inward side faces the optical film and the outward side is opposite to the inward side. The spacer supports the optical film set and is mounted onto the bottom plate of the backlight module from the outward side of the bottom plate.