The paper describes the further improvement of interferometric laser imaging for droplet sizing technique that is the novel Lagrangian approach for the measurement of droplet size and velocity vector by means of a high-speed and high-resolution camera in conjunction with the double-pulsed high-frequency Nd:YLF laser. Measurement uncertainties due to the geometric optical approximation as well as the refractive index modulation were numerically analyzed. The technique was applied to the measurement of the evaporating ethanol spray. The size transition of the single droplet within a few milliseconds was experimentally investigated. The results led us to evaluate the mass transfer rate at the gas-liquid interface of the individual droplet.