Nowadays, unmanned air vehicle (UAV) are considered as popular devices for a wide variety of mission, such as detection and identification. Besides their low cost and other weight and dimensional merits, their advantage of being unmanned make them more suitable and reliable in comparison with other alternatives to accomplish their missions. The Micro Air Vehicle (MAV) are a subset of UAVs with sizes smaller than 500mm and weights under 500g and are designed and made in four categories, namely, fixed wing, VTOL (Vertical Take off Landing), flapping wing and rotary wing. The type studied in the present work is a flapping wing MAV which has a similar structure as birds. The research on flapping wing MAVs has shown that these types of air vehicles have more complexities compared with fixed and rotary wings mainly due to their complex aerodynamics. As a result, there are fewer researches available in this subject. Biologic iiration indicates that flying through flapping wings presents unique maneuverability advantages. There are fundamental challenges for fixed and rotary wings to fly reliably when their sizes are reduced. When the wing area is reduced, a flow transition to low Reynolds number occurs which reduces the aerodynamic wing efficiency. A flapping wing MAV has the potential to benefit from the advantages of other MAV types and eliminates their disadvantages. In the present work, a comprehensive study on flapping wing MAVs is inducted first, and then a new conceptual design procedure is proposed for flapping wing MAVs. It should be mentioned that presently there is no well documented and established design procedure for flapping wing MAVs and these tasks are mainly done through try and error techniques. The main focus of the current research is on conceptual design and the sizing of flapping wing MAVs which results in determining the wing geometrical parameters. In addition, the dynamical and kinematical equation for different flying modes such as flapping and gliding are derived. More over for the first time (to the best knowledge of the author) a constraint analysis based on the MAV mission is performed. The aim of this analysis is to determine the design space. The shape of the wings (planforms) is iired by the shape of real bird wings and their lift and thrust is determined through the use of strip theory. The determination of the flapping frequency and the weight estimation of the flapping wing MAVs are other tasks performed in the present sizing procedure. Finally, based on the presented design procedure, a flapping wing MAV with a wingspan of 70cm and a weight of 382g is designed and manufactured. All aerodynamic calculations, stability analysis and mechanism design are performed to validate the proposed design procedure. Another contribution of the present research is the introduction of a new conceptual design procedure for design and manufacture flapping wing MAVs iired by living birds. Keywords Micro Air Vehicle, Flapping Wing, Conceptual design, Sizing, Strip Theory, Flapping Mechanism