An exemplary backlight module (20) includes a light source (23), a light guide plate (21), a light source reflector (22), and a holding device (24). The light guide plate includes a light incident surface (211). The light source is disposed adjacent to the light incident surface. The light source reflector attaches to the light guide plate, and includes a fixing hole (224). The holding device engages with the light source reflector at the fixing hole and restrains the light source in position a predetermined maximum distance away from the light source reflector.