The size and velocity of atomized droplets are simultaneously measured by dual-beam light-scatter interferometry. The relationship of scattered beam intensity against a broad range of particle size parameters (10(1) similar to 10(3)) is theoretically analyzed, and the effect of the aperture of collimating lens is numerically studied to clarify the range to show the linear relation. It is implied that this measurement is available for particles of diameter 10 similar to 200 mu m when the numerical aperture of focusing lens is 5.2 x 10(-2) in the optical system. This method is applied to the cold model of the atomized droplets. The behavior of the velocity and the droplet particle size measured by using the open optical system which has a comparatively long focus length corresponded to the conventional one.