Nanoparticles of cadmium sulfide have been synthesized by a microemulsion method two microemulsions cantaining cadmium ions and containing sulfide ions respectably were mixed to form cadmium sulfide nanoparticles. In order to investigate the influences of water to surfactant molar ratio(W) on the particle size, we fixed [AOT], and the initial molar concentration of Cd²⁺ and S²⁺ and only changed W. The effects of varying the type of continuous oil phase on the particle size have been studied. The time-course variation in the mean particle size was measured by UV-visible absorption spectroscopy.