Platinum nanoparticles were synthesized by mixing of two micro emulsions. Synthesized platinum nanoparticles were characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Nanoparticles stability was analyzed using transmission and backscattering profiles of colloidal platinum solution. Catalytic activity of synthesized colloidal platinum nanoparticles was checked for the reduction of 4-nitrophenol and 4-nitrobenzo 15-crown compound and monitored by ultraviolet-visible absorption spectroscopy. Effects of amount of catalyst and amount of reducing agent were also studied. The reaction was found to follow pseudo-first-order kinetics with respect to nitro compound.