This paper presents an electrically powered Micro Air Vehicle (MAV) with a flexible wing integrated with on-board electronic components that is built at Tsinghua University. The low aspect ratio wing, adopting the airfoil of S5010 and Zimmerman shape, is made up of a flexible printed circuit membrane (FPCM) that covers a thin carbon fiber skeleton. The real MAV prototype is tested in a low-speed wind tunnel in order to evaluate its aerodynamic characteristics. The comparing experiments are conducted on the flexible wing and its rigid counterpart with the same size and the same wing shape to illustrate the aerodynamic advantages of the flexible wing. The results of the wind tunnel experiments indicate that the flexible wing has a larger angle of stall, bigger maximum lift coefficient than the rigid one. However, the lift-drag ratio of the flexible wing varies in a complex way because the flexible wing also increases the drag with the lift growth. The FPCM functions as both the skin of the aircraft wing and the supporting substrate for the electronic components, such as micro hot-film flow speed sensors that are used to determine 3 fundamental flight parameters: air speed, angle of attack and sideslip angle. In addition, most of the signal processing circuits is distributed on the FPCM, which remarkably reduces the autopilot load. The dimensions of a homemade autopilot that is separately installed in the fuselage are 35x20xl2mm with the weight of 6g. Through experiments of real flights, the turning, climbing, maneuverability and wind resistant ability of the MAV are tested. The flight results show that the MAV can fly with good stability and maneuverability.