An MEMS variable optical attenuator includes a substrate having a planar surface, a micro-electric actuator arranged on the planar surface of the substrate, a pair of coaxially aligned optical waveguides having a receiving end and a transmitting end, respectively, and an optical shutter movable to a predetermined position between the receiving end and the transmitting end of the optical waveguides, and driven by the micro-electric actuator. A surface layer is formed on the optical shutter, has reflectivity less than 80% so as to allow incident light beams to partially transmit thereinto, and further has a sufficient light extinction ratio, thereby extinguishing the partially transmitted light beams therein.