The hydrogen adsorption isotherms of activated carbon fiber loaded with platinum (Pt-ACF) in the 303-673 K range indicated that a temperature above 573 K was required to give rise to an increase in the amount of adsorbed hydrogen due to the spillover phenomenon. Two peaks at 800 and 1200 K in the D-2 desorption profile of Pt-ACF clarified that two kinds of sites for adsorption or bonding of spiltover deuterium exist on the carbon surface.