The effects of water content on the growth rate and the final particle size of AgCl nanoparticles in a reversed micelle (RM) system of polyoxyethylene (6) nonylphenyl ether (NP-6)/water/cyclohexane were investigated using a double-jet technique, in which RM solutions of AgNO3 and KCl were added concurrently to a RM solution containing the excess concentration of chloride ion. As a result, the particle growth rate and the final particle size at a constant Rw (equivalent to [water]/[surfactant]) below 5 were found to be in excellent agreement with our theoretical prediction based on a dynamic Ostwald ripening mechanism governed by the overall solubility of the solid and the diffusivity of the reversed micelles, whereas the final particle size was far beyond the size of the water pool of a reversed micelle. Thus, the dramatic reduction of the particle size in the RM system can be explained by the drastic reduction of the overall solubility of the solid and the small diffusivity of the bulky reversed micelles as a carrier of silver ion, and not by the size of the water pool of a reversed micelle as conventionally explained. Some additional contribution of a coagulation process was also suggested in a high Rw rang above 5. Significant coagulation of A-Cl particles was observed in a RM system with AOT in place of NP-6 even under the standard conditions for the NP-6 system. (c) 2005 Elsevier Inc. All rights reserved.