An exemplary backlight module (2) includes a light guide plate (21) and a light source (23). The light guide plate includes a main body, a protrusion (217) extending from an end of the main body, a main light emitting surface (211), and a light incident surface (215) at the end of the main body. Wherein one side of the protrusion forms a part of the light emitting surface, another side (2171) of the protrusion is adjacent to the light incident surface. The protrusion and the light incident surface cooperatively form an accommodating space. The light source is substantially received in the accommodating space.