This paper reports a Pitot tube type airflow sensor, which achieves both high sensitivity and water resistance. The proposed Pitot tube is composed of piezoresistive cantilevers as differential pressure sensing elements and nano-hole arrays as waterproof elements. The nano-hole arrays are attached to the air inlets, which are located the tip of the tube and sides of the sphere. When airflow is applied to the Pitot tube, air passes through the nano-hole arrays, and differential pressure between two inlets acts on the piezoresistive cantilevers. On the other hand, when locating in water, the nano-hole arrays protect the water penetration into the tube. The Pitot tube will be used for the airspeed measurement of flying marine birds.