La1-XCaXMnO3 (X = 0.0, 0.2, 0.4, and 0.6) perovskite oxides were synthesized using the citrate gel method. Thermogravimetry and differential thermal analyses, x-ray diffraction, scanning electron microscopy, and specific surface area results were used for characterization of the perovskite powders obtained. Also, the average manganese valence state and delta-oxygen non-stoichiometry in series compounds were determined by the chemical analysis. Catalytic activities of these perovskites were examined for the peroxide decomposition reaction. It was observed that the catalytic activity was improved with increasing calcium content in the catalyst and it is suggested that factors such as delta-oxygen non-stoichiometry and average manganese valence state were responsible for the catalytic activity of these materials.