TiO2 supported transition metal oxides were investigated for the direct decomposition of nitrogen oxides (NOx) at lower temperatures. The results showed that the catalytic performance strongly depends on the kind of transition metal oxide deposited on the TiO2. Among the various catalysts examined, Mn/TiO2 and Co/TiO2 exhibited relatively high NOx conversion at lower temperatures in the presence of 3 vol % O-2. The oxygen in the reaction stream had a positive impact on the NOx decomposition over the Mn/TiO2 catalyst. We have not observed any TiO2 phase conversion from anatase to rutile in the Mn/TiO2 during the NOx decomposition reaction at different temperatures (100-350 degrees C). NOx decomposition activity was shown to be governed by the surface labile oxygen rather than the gas phase oxygen. The Mn/TiO2 catalyst exhibited a good resistance to 10 vol % H2O and 100 ppm of SO2.