Adsorption of PtCl62- anions on surface of carbon black was studied. It was found that the absence of surface oxygen groups led to a higher Pt loading amount, and the Pt loading amount would decrease as using a higher H2PtCl6 impregnating solution concentration. The pi sites in the basal planes of carbon black surface act as the chemical adsorption sites, playing a more important role than surface oxygen groups in PtCl62- adsorption. Adsorption of large amounts of H3O+ in the pi sites would lead to a decrease of chemical adsorption capacity.