The preparation of ultrafine CdS and ZnS particles is studied by combining particle preparation in reverse micelles and Liquid-liquid extraction. Sodium bis(2-ethylhexyl)sulfosuccinate (AOT) was added to the organic phase solution containing the extractant-metal ion complex, and either a reverse micellar solution containing Na2S or simply H2S gas was then added to the solution. The process of particle formation was followed by means of measurement of the absorption spectra. The hey step is the release of the metal ion from the complex. The rate for the release governs the rate for particle growth, and thus controls the particle size. When the complex is stabilized too much. no particles are formed. The preparation of CdS and ZnS particles at high concentrations was also carried out.