Stable Pt sols were prepared by the radiolytic reduction of H2PtCl4 in presence of protective water soluble polymer gelatin. The particle size and morphology were determined by TEM and found to be in the nm range. The catalytic activity of the sols was tested by hydrogenation of C2H4 at room temperature and compared with the standard Pt/Al2O3 catalyst. The effects of CH3OH addition and glass support on the rate of the catalytic reaction were also investigated.