A back light module is provided. The back light module comprises a light-guiding plate, a side light source and a bottom light source. The side light source is positioned on one side facing a side surface of the light-guiding plate. The bottom light source is positioned on a bottom surface of the light-guiding plate. Light from the side light source and the bottom light source both emerge from a top surface of the light-guiding plate. The side light source and the bottom light source together provide a bright surface light source that illuminates a liquid crystal display to produce a better display effect. In addition, this invention also provides e liquid crystal display comprising a transmissive or transflective liquid crystal display panel and the aforementioned back light module.