A backlight module and a liquid crystal display are provided. The backlight module includes a plastic frame. The sidewalls of the plastic frame have an adjustable length. Each sidewall having the adjustable length includes at least two separated member slidably connected together. The present invention may flexibly set the plastic frame according to the size of the liquid crystal display, and need not specially configure the moulds to produce the plastic frames for the different sizes of the liquid crystal display, thereby not only reducing the cost, but also increasing the manufacture efficiency.