A light guide plate (2) includes a light output surface (20) and a bottom surface (22) opposite to the light output surface. The bottom surface defines a plurality of V-shaped grooves (221) thereat, and each of the V-shaped grooves is bounded by a pair of walls along a length thereof. The walls cooperatively form an apex angle, and each of the V-shaped grooves has an apex angle in a range of 67° to 85°. With such configuration, light beams input to the light guide plate can be directed and transmitted within the light guide plate toward particular desired directions. Such directions are typically directions toward a viewer of an associated liquid crystal display panel. Accordingly, a backlight module that employs the light guide plate may advantageously obtain more efficient utilization of illumination and greater brightness in particular desired directions.