An exemplary optical plate includes at least one transparent plate unit. The transparent plate unit includes a first surface, a second surface, a plurality of conical frustum protrusions, a plurality of spherical protrusions and a lamp-receiving portion. The second surface is opposite to the first surface. The conical frustum protrusions are formed at the first surface. The spherical protrusions are formed at the second surface. The lamp-receiving portion is defined in at least one of the first surface and the second surface. A backlight module using the present optical plate is also provided.