Platinum was supported on silica gel from tetraammineplatinum (II) dichloride and hydroxyopentaammineplatinum (IV) trichloride, hereafter referred to simply as Pt (II) ammine and Pt (IV) ammine, and their adsorption behavior and the platinum surface area were compared. Various pHs adjusted by ammonia were applied for ion exchange adsorption of the platinum complex ions onto silica gel. The maximum value of Pt (IV) ammine adsorption appeared as a relation of pH though the adsorption of Pt (II) ammine was increased with increasing pH. The direct hydrogen reduction of the adsorbed complex ions into Pt metal gave a higher platinum surface area as compared with calcination pretreatment in air. The platinum surface area from Pt (IV) ammine was decreased with increasing pH over 7.2 though the surface area from Pt (II) ammine was independent of pH. Pt (IV) ammine adsorption in the range of pH < 7.2 gave a higher platinum surface area than Pt (II) ammine.