Silver nanoparticles with sizes less then 10 nm have been formed in natural rubber films by reduction of silver salt via UV exposure and are time dependent. The proteins present in natural rubber latex are believed to play an important role in the growth and stabilization of the particles. High concentrations of stabilized silver nanoparticles are found at the interfacial region of the rubber particles where mixing of proteins occurs. However, aggregates of nanoparticles of metallic silver are observed in DPNR and natural rubber containing surfactant SDS but not in samples where silver salt was added to NR before SDS. In summary, protein is essential for the stabilization of silver nanoparticles in natural rubber.