A backlight module includes a light source, a light guide plate and a reflector. The light guide plate includes a light incidence surface, a light-emitting surface opposite to the light incidence surface, and a pair of side surfaces connecting the light incidence surface to the light-emitting surface. The light-emitting surface of the light guide plate includes a groove formed therein. The reflector is placed between the light source and the light incidence surface of the light guide plate, and located corresponding to the groove of the light-emitting surface of the light guide plate. The reflector includes a light-receiving surface. The light source is facing the light-receiving surface of the reflector.