Mn-doped La0.8Sr0.2CoO3 perovskite oxides (La0.8Sr0.2Co1-xMnxO3; x = 0, 0.1, 0.3, 0.5) were synthesized by a modified sol-gel method. The phase-pure oxides were obtained. CoO and carbonates were formed on the surface of La0.8Sr0.2CoO3. With increasing doping content, these impurities were reduced while the stability of the perovskite structure was improved. The valence state of B-site ions and the amount of absorbed oxygen were influenced by Mn doping. The catalytic activity of the perovskite catalysts was investigated for CO oxidation and simultaneous removal of CO, C3H8, and NO. For CO and NO removal, La0.8Sr0.2Co0.9Mn0.1O3 exhibited the best performance. For C3H8 removal, the reactivity was promoted linearly with the doping content. The structure-activity relationship is also discussed.