The design of the actuating mechanism of a biologically inspired flapping wing UAV is addressed. Several configurations able to reproduce the desired flapping-wing kinematics are analyzed and an optimization study is conducted to select the best configuration. The optimization results are used as the starting point for the design of the different structural components of the flapping mechanism. During the mechanism design stage, the linkages are optimized to match the desired wing’s motion during a flapping cycle. A structural and durability analysis is then conducted to verify that the mechanism and its components are able to withstand the aerodynamic and inertial loads.