After the initial precipitation of ultrafine AgCl particles caused by instantaneous mixing of silver nitrate and potassium chloride in a reverse micelle system of polyoxyethylene (6) nonylphenyl ether/water/cyclohexane, the AgCl nanoparticles were found to grow through Ostwald ripening, and not by the coagulation process, from their growth rate independent of the initial particle density within our experimental range.