An exemplary optical plate includes at least one transparent plate unit. The transparent plate unit includes a light output surface, a bottom surface, a plurality of enclosing V-shaped protrusions, a plurality of microstructures and at least one lamp-receiving portion. The light output surface is opposite to the bottom surface. The enclosing V-shaped protrusions are formed on the bottom surface. The microstructures are formed on the light output surface. The lamp-receiving portion is defined in the bottom surface. A backlight module using the present optical plate is also provided.