The objective of this project is to develop a battery-powered ornithopter (flapping-wing) Micro Aerial Vehicle (MAV) with MEMS wings. In this paper, we present a novel MEMS-based wing technology that we developed using titanium-alloy metal as wingframe and parylene C as wing membrane. MEMS technology enables systematic research in terms of repeatablility, size control, and weight minimization. We constructed a high quality low-speed wind tunnel with velocity uniformity of 0.5% and speeds from 1 m/s to 10 m/s. We have tested and have studied the unsteady-state aerodynamics of various types of MEMS wings. Finally, we built lightweight omithopters with electric-powered transmission system and have demonstrated successful free flights of with flight duration ranges from 5 to 18 seconds.