Size measurement of micron-sized metal droplet is of great demand in industrial applications, e.g., 3D printing and metal propellant. A dual-beam interferometric particle imaging (DIPI) technique is developed to measure the size of opaque metal droplet, which is adapted from the traditional interferometric particle imaging (IPI) for transparent particles. In DIPI, the studied metal droplet is illuminated by two laser beams from different views, and the laser beams are reflected on the surface of the droplet. An interference pattern of the two reflections is yielded in the far-field that was capable to derive the size of aim droplet. The principle of DIPI is formulated in the framework of physical optics, with system configuration, modeling and data processing algorithm presented. A DIPI system is established to characterize the gallium droplet with size ranging from 300 pm to 500 pm experimentally, and the measured sizes with DIPI is compared with those obtained simultaneously by digital inline holography, which is a standard tool for particle measurement. Comparison shows that the measurements with these two methods are highly consistent, with a standard deviation of 1.7%. DIPI has been demonstrated with high measurement accuracy and flexible implementation of the one-sided arrangement. (C) 2019 Published by Elsevier B.V.