A backlight module includes a reflector, a light guide plate and a film. The reflector includes a supporting plate and two extending portions, and the extending portions are located on two opposite sides of the supporting plate, respectively. The film includes a main body and two positioning portions, and the positioning portions are located on two opposite sides of the main body, respectively. The light guide plate is located between the supporting plate and the main body. The main body corresponds to the supporting plate, and the positioning portions correspond to the extending portions. The extending portions are bent toward the main body, and the positioning portions are bent toward the supporting plate. The positioning portions are at least partially overlapped with and are fixed to the extending portions, respectively.