This paper presents an autonomous formation flight algorithm for micro aerial vehicles (MAVs) and its experiment results. We choose the leader follower scheme for formation flight as it is more appropriate for tracking arbitrary maneuvering of the leader in a formation. The sensing of other vehicles in the formation is achieved by sharing the vehicles' states using a high-speed peer-to-peer radio data link. The designed guidance law is combined with a PD controller for tracking heading, velocity and altitude commands. A series of test flights were performed to validate the proposed formation guidance law. The test result confirms that the proposed formation flight algorithm is feasible to yield satisfactory results.