The effects of doping of Al2O3-supported nickel and manganeseoxides with La2O3 on their surface and catalytic properties were investigated using nitrogen adsorption at -196degreesC, the oxidation of CO by O-2 at 150-200degreesC, and the decomposition of H2O2 at 30-50degreesC. The dopant concentration was varied between 1.0 and 6.0 mol%. Pure and variously doped solids were prepared by wet impregnation method using finely powdered Al(OH)(3) solid followed by treating with different amounts of lanthanum nitrate. The lanthanum nitrate-treated were divided into two portions. The first portion was treated with a fixed amount of nickel nitrate dissolved in the least amount of distilled water. The second portion was treated with a known amount of manganese nitrate. Pure and doped solids were calcined at 400-700degreesC. The results obtained revealed that the doping process of the investigated solids decreased the degree of crystallinity and particle size of both NiO and Mn2O3 phases. La2O3-doping of investigated systems increased their catalytic activities towards CO-oxidation by O-2 and H2O2 decomposition to an extent proportional to the amount of dopant added. The doping process did not modify the activation energy of the catalyzed reaction but increased the concentration of catalytically active constituents taking part in the catalytic processes without changing their energetic nature. (C) 2003 Elsevier B.V. All rights reserved.