A series of platinum-tin catalysts supported on carbon have been prepared from organometallic precursors using surface organometallic chemistry (SOMC). The catalysts were characterized using chemisorption, transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), anti cyclic voltammetry. The addition of tin to Pt/C suppresses chemisorption of both hydrogen and carbon monoxide, with a rapid decrease on addition of just a small amount of tin, leveling off to give a plateau at higher lending. TEM, EDX. and XPS provide evidence that the platinum and tin occur together on the support and that on exposure to air the catalysts consist mainly of metallic platinum in association with tin oxide. A catalyst prepared using SOMC and another of similar loading prepared using conventional precipitation were compared for thr electro-oxidation of adsorbed carbon monoxide using cyclic voltammetry. The catalyst prepared using SOMC showed enhanced activity with a larger decrease in the onset potential of carbon monoxide oxidation compared to Pt/C. Comparison of a range of carbon support platinum-tin catalysts with different loading prepared using SOMC showed a decrease in the onset potential for the catalyst at low loading with no further significant decrease in potential on addition of further tin. The peak intensities, however changed significantly with an increase in loading.