A carbon-supported platinum electrocatalyst was modified with molybdenurr using surface organometallic chemistry. The catalyst was characterized using transmission electron microscopy, cyclic voltammetry (CV), polarization studies, and in situ fluorescence extended X-ray absorption fine structure (EXAFS) studies. The CV and polarization studies show that CO oxidation starts at low overpotentials. similar to those of a conventially prepared PtCoMo/C electrocatalyst. EXAFS at the Mo K edge recorded at 0.65 V show that the Mo exists as an oxide species associated with the Pt surface with a Mo-O distance of 1.75 Angstrom. At 0.05 V this oxide is reduced with the formation of a metal-metal bond between the Mo and Ft, with a bond distance of 2.63 Angstrom.