The performance of a laser-based optical technique to measure simultaneously the velocity and equivalent diameter of nonspherical particles was evaluated. The size information was provided by the absolute intensity of diffractively scattered light by a particle crossing a single laser beam, which is concentric with a laser Doppler probe volume. The response curve (size-intensity relationship) of the technique was estimated by calculations using the Fraunhofer approximation. Experiments with spherical glass and polyethylene and non-spherical metal and ceramic particles ranging from 20 to 200 mum confirmed the operation of the technique and in all the measurements the maximum error of the average diameter was 10 mum as compared with size information provided by a microscope.