The catalytic decomposition of nitrous oxide(N2O) and nitric oxide(NO) into nitrogen and oxygen in the presence of carbon monoxide have been performed over a fixed bed of mixed metal oxide(MMO) catalysts derived by calcination from hydrotalcite-type precursors. In the case of simultaneous decomposition of NO and O2O, No decomposition proceeds faster than N2O. Moreover, simultaneous decomposition efficiencies of NO and N2O are better as compared with single decomposition efficiency of NO or N2O, The catalytic activities for NO and N2O decomposition in the presence of CO were-proven having full conversion efficiencies even at tne temperatures under 250℃.