Numerical simulations were performed to investigate the flowfield around a flexible flapping-wing micro air vehicle using an in-house-developed computational fluid dynamics solver. To include the dynamics of the flexible wings and its impact on the aerodynamic behavior of the micro air vehicle, the wing-deformation pattern during flapping was experimentally determined by a stereovision measurement. These data were subsequently interpolated to be employed as prescribed flapping kinematics in the numerical flow simulations, using a computational fluid dynamics solver that is based on a deformable overset-grid method. The computational results of the hovering configuration provide a quantitative prediction of the unsteady aerodynamics of the flapping-wing micro air vehicle in terms of aerodynamic force production and flow structures. The formation and evolution of the leading-/trailing-edge vortex and tip vortex were visualized. Additionally, by introducing an incoming freestream flow velocity in the simulations, the flowstructure related to the forward-flight configuration is investigated. The forces and the flow structures are compared with the experimental results from force and digital-particle-image-velocimetry measurements; a good agreement was illustrated that further evidenced the capability of the numerical methodology proposed in the present study.