A series of strontium-lanthanum oxide mixed manganese nodules were prepared and characterized by X-ray diffraction, nitrogen adsorption-desorption, electrical conductivity, and surface excess oxygen. X-ray diffraction patterns confirm the formation of perovskite-type oxides at low strontium content (x less than or equal to 0.5, in La(1-x)Sr(x)MO(3), where M denotes the transition metal present in nodules), whereas at 0.6 less than or equal to x less than or equal to 0.8, La2O3 and SrO are detected in addition to the perovskite-type oxides. The catalytic activities for hydrogen peroxide decomposition and carbon monoxide oxidation increase with an increase in Sr substitution for La, attain a maximum at x = 0.4, and then decrease with further increase in Sr. The activities have been correlated with various physicochemical properties.