The kinetics of H2O2 decomposition have been investigated using ZrO2 supported with transition metal ions including CuII, AgI , HgII, CoII, MnII, NiII and FeIII. At pH = 6.8, the reaction rate exhibits a ®rst order dependence on the initial H2O2 concentration at low concentrations. The order of activity of the dierent catalysts is strongly dependent on the [H2O2]0 used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting eect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HOá 2 radicals from the peroxo-intermediate as the rate-determining step.