Perovskite-type La0.8Sr0.2CoO3 mixed oxides were prepared by D,L-alanine solution combustion synthesis and used successfully in CH4 combustion as catalysts. These samples were characterized by means of XRD, FTIR, BET, and H-2-TPR methods. The effects of stoichiometric ratio (phi) of organic fuel to oxidizer on the structure and catalytic activities of the catalysts were studied. The results indicate that all La0.8Sr0.2CoO3 mixed oxides with different phi have perovskite structures. Their structures and catalytic activities vary along with the change of phi. The catalytic activity of La0.8Sr0.2CoO3 mixed oxide with phi = 1.52 is the best among all the samples, whose T-50 and T-100 (the temperatures of methane conversions reaching 50 and 100%, respectively) are respectively 470 degrees C and 550 degrees C, which can be explained in terms of the smaller of average crystal size, higher specific surface area, bigger lattice distortion, lower activation energy, and higher mobility of chemically adsorbed oxygen on the surface and vacancy of the catalysts.