Perovskites are very thermally stable mixed oxides, frequently used as oxidation catalysts in spite of their relatively low surface area. In order to increase the area the sol-gel method has been used, with malic acid as complexing agent and pH adjustment of the starting solution, to prepare the LaCoO3 perovskite, used as a reference, and other perovskites in which the La cation has been partially replaced (20% molar) by Ca, Sr or Ba cations. Additionally, the cooling rate of the fresh catalysts, from the calcination temperature to room temperature, has been used as a parameter in the method of preparation. The catalysts were characterized by BET area, DRX, TG, DTA, and SEM-EDX. Catalytic activity was tested in a fixed bed flow reactor using the oxidation of CO with O2 reaction. The DRX studies confirmed the presence of a single phase with perovskite structure in the catalysts calcined at 550 C, and the additional studies confirmed that very uniform catalysts with great thermal stability were obtained. Substitution of La by group II cations and the method of preparation make it possible to obtain perovskites with large surface area and excellent catalytic activity for CO oxidation, reaching maximum conversion values, close to 100%, at temperatures of about 200 C. Changes in post-calcination cooling rate did not produce significant changes in the surface area or in the catalytic activity of the catalysts, except when Ba-substituted catalysts were used