Various aspects of nanoparticle precipitation in gas-reverse micellar systems have been studied. The experimental system chosen for investigation deals with the precipitation of CaCO3 nanoparticles. The effect of operating variables, such as water-to-surfactant molar ratio, different continuous phases, surfactant concentration and stirring speed, have been investigated experimentally. The results indicate that using low concentrations of Ca(OH)2particles outside the micelles, low surfactant concentrations, low stirring speeds and water-to-surfactant molar ratios lead to the formation of smaller nanoparticles in gas-reverse micellar systems.