The authors investigate the fabrication of components of MAVs (micro aerial vehicles) with 21.6 cm wingspan by using precision injection molding. In this study. a bio-mimicking flapping MAV was shaped like birds. The author also analyzes the degree of asymmetry flapping mechanism, designs ten different plastic components (for the gear transmission module) which are as light as possible, and guarantees the smooth flapping motion as well. Thereafter the injection flow analysis in the multi-mold cavity and the fabrication parameters of the molding process according to these data has been done. The finished MAV components finally verify the design and process flow of the precision injection molding. After the MAV was assembled and tested with the fore-mentioned plastic components, a successful flight record of 367 sec was created. Additionally we designed a bird-like fuselage with 19.5cm in length, for horizontal tail, and for vertical airfoil. After the bird-like MAV was assembled and tested, it sustains a successful flight for 230 sec as well. In summary, the design methodology of a polymeric bird-like MAV is proved, and the precision injection molding technique still shows its feasibility in real application to flapping MAVs herein.