A backlight module (2) includes a light source (21) and a light guide plate (23). The light source includes a lamp (231) and two electrode cases (233), the two electrode cases engage with opposite ends of the lamp. The light guide plate includes a light output surface (212), a bottom surface (213), two adjacent light incident surfaces (211), two side surfaces (214), and two holding devices (215). The two holding devices are respectively provided at diagonally opposite corners of the light guide plate, where the light incident surfaces are respectively adjacent the side surfaces, and the holding devices are for retaining electrode cases. The light source is disposed adjacent to the light incident surfaces. The lamp are not liable to shock, so the lamp can not be damaged. Further, the backlight module eliminates the need for rubber rings. Thereby reducing the cost of the backlight module.