LaxSr2-xMnO4 (0 <= x < 0.8) oxides were synthesized and single-phase K2NiF4-type oxides were obtained in the range of 0.1 <= x < 0.5. The catalytic activity of LaxSr2-xMnO4 for NO-CO reaction increased with increasing x in the range of solubility limit of La. La0.5Sr1.5MnO4 showed the highest activity among LaxSr2-xMnO4 prepared in this study, but its activity was inferior to perovskite-type La0.5Sr0.5MnO3. Among the Pd-loaded catalysts, however, Pd/La0.8Sr1.2MnO4 showed the higher activity and the selectivity to N-2 than Pd/La0.5Sr0.5MnO3 and Pd/gamma-Al2O3. The excellent catalytic performance of Pd/La0.2Sr1.2MnO4 could be ascribable to the formation of SrPd3O4 which was detected by XRD in the catalyst but not in the other two catalysts. (c) 2006 Elsevier B.V. All rights reserved.