A backlight module includes a light guide plate, a light source and a ventilating tube. The light guide plate includes a light exiting surface and a light incident surface adjacent the light exiting surface. The light source includes a plurality of light emitting diodes facing the light incident surface of the light guide plate. The ventilating tube is thermally connected to the light source. The ventilating tube defines an air inlet in one first end, an air outlet in an opposite second end, and an air passage channel interconnecting the air inlet to the air outlet. The air outlet is at a higher altitude than the air inlet along a gravitational force direction.