We have developed an insect-size X-wing flapping Micro Air Vehicle (MAV) with a body-length of approximately 6 cm. To quantify the aerodynamic performance of the MAV with a specific focus on the clap and fling mechanism we measured the thrust/lift forces in tethered and free (level) flights. Our tethered flight results show that the MAV is capable to create a thrust force 1.3 times greater than its weight. In the free (level) flight, the stroke plane angle is observed to be around 45 degrees corresponding with a flapping frequency of approximately 25 Hz. Furthermore, we find that the MAV is able to perform the level flight when a static thrust produced is over 0.8 times its weight and that appropriate flexibility of the wing can be a crucial factor in affecting the thrust production to keep it stay on airborne.