A backlight module includes a light guide plate, at least one light source, and a light-reflecting plate. The light guide plate includes a light-emitting surface, a bottom surface, a light-incident surface, and a guiding tilt surface. One end of guiding tilt surface and light-emitting surface are intersected at a first boundary, and the other end connects to a top edge of light-incident surface. The guiding tilt surface extends toward a direction of protruding the light-emitting surface. The horizontal distance between the first boundary and light-incident surface is L. The light-reflecting plate is disposed under the bottom surface. When the horizontal distance d between light-incident surface and an end of light-reflecting plate near light-incident surface is less than L, the horizontal distance between a vertical projection of the end on light-emitting surface and first boundary is not more than 0.5 mm. When d is more than L, x is at least 0.5 mm.