Nanosized platinum particles have been produced in AOT/cyclohexane/water microemulsion system. The effects of precursor (H2PtCl6) concentration, reducing agent (N2H4) concentration and W parameter value (W = [water]/[surfactant]) on the synthesized platinum nanoparticle size have been investi gated. The synthesized Pt nanoparticles were characterized by using UVvisible absorption spectroscopy and scanning electron microscopy. The obtained data showed that the size of the synthesized Pt nanoparticles can be increased by increasing precursor or reducing agent concentrations as well as that of the water/surfactant molar ratio