An optical plate includes a substrate having a light emitting surface, a rear surface opposite to the light emitting surface, and a plurality of microstructures that cooperatively define the light emitting surface and each of which parallelly extends in a light traveling direction. Each of the microstructures includes first and second convex portions and a concave portion disposed between and interconnecting the first and second convex portions, and two adjacent ones of the microstructures are connected. Intersections between the microstructures cooperatively define an imaginary plane, and a lowest point of the concave portion is disposed at one side of the imaginary plane opposite to the rear surface of the substrate.