In order to study heat transfer with a mist flow and the vapor condensation, it is strongly desirable to measure locally droplet sizes and the velocities. A new method has been developed for this purpose, in which capacity changes is produced by movement of droplet along the double needle probe. The applicable ranges of this method are: droplet size range; 1. 9～3.1 mm, and the velocity range; 0.5～1.4 m/sec. In the measurement of the droplet size profile for the spray in a vertical channel, the measured and pre-set maximum mist sizes; 300μm, agree within ±10%.