Disclosed are back light module and display device. The back light module comprises a light source, a back plate, a light guide plate and a positioning member. The back plate is formed with a frame for receiving the light guide plate; the light source is provided on an inside surface of a side panel of the back plate and oppositely to a light incident surface of the light guide plate. The positioning member is provided at both ends of the back plate on a side where the light source is formed and interposed between the light incident surface of light guide plate and the light source. The back light module herein ensures that the gap between the light incident surface of light guide plate and the light source has fixed value, thereby improving evenness of display images of display device.