This paper describes a miniaturized particle sizing velocimeter developed and built by MetroLaser to measure the spatial and temporal distributions of particle size and velocity. The instrument is the first of its kind to utilize the pulse displacement technique (PDT) to measure particle size. PDT is based on the detection of scattered refraction and reflection pulses which sweep past a detector at different times as a particle traverses a narrow laser sheet. In conjunction with Mie scattering and a time-of-fight velocity measuring technique, the instrument provides detailed distributions of particle size from 2 mu m to 6000 mu m in two optical configurations, and particle velocity from 0.5 m/s to 150 m/s. This paper summarizes the theoretical foundation of PDT which allows the calculation of particle diameter from Various optical parameters such as refractive index and collection angle. An overview of the instrument is presented, followed by a brief description of the miniaturized optical probe. The processing of data is described and lastly, the results of experimental studies are presented which verify the accuracy and versatility of the instrument.