Various authorsl-9 have \lied semi-conductors IDd insuJators such II chuc:oal, IiIic:a gel and alu~ gel as promoters for the decomposition of hydrogen peroxide by platinum catalysts. Walker et al 0 have used glassy carbon II a support. In the present work, it WII found that small quatities of rare earth oxides, cerium (IV) oxide, lanthlDum (1m oxide, pmseodymium (II) oxide, thaDium (IU) oxide and samarium (III) oxide act II strong promoters in the decomposition of aqueous hydrogen peroxide by finely divided platinum. The decomposition products WeJe followed by a volu­metric method. In generll1. the activity of a constant amount of platinum first rises to a peak point and subsequently sinks II the ratio of promoters to the catalyst in further increased. The catalytic activi­ties of these promoters follow the sequence: ceO~ L'203> Pr6011> n203> Sm203' The apparent activation energy of the decomposition of hydrogen peroxide in aqueous solutions have been determined at various temperatures. It is shown that there is a dependence of the activation energy on the temperature, A strict logarithmic dependence of the activation energy results in the disappearence of the promoter action of the supports at low temperatures. The surfaCe of the oxides studied WII thus shown to be irregulady heterogenous.