Polyacrylamide nanoparticles of different size (<100 nm) were prepared in reverse micelles under various dynamic conditions of micellar systems. The nanoparticles were always larger than the aqueous core in which they were formed; however, the size of the nanoparticles could be controlled if the interdroplet interaction and coalescence rate in reverse micelles were regulated. Factors such as interfacial rigidity of the droplets, size of the aqueous core, temperature, and concentrations of acrylamide (monomer) and N,N’-methylenebisacrylamide (crosslinking agent) have a profound effect on the size of nanoparticles. By adjustment of these parameters in reverse micelles, nanoparticles ranging from about 10 to more than 100 nm have been prepared.