Abstract: A series of Mn-Mg-Al-O hydrotalcite precursors with M(II)/Al(III) molar ratio of 3 were prepared by co-precipitation method; corresponding mixed oxides were obtained after calcinations at 500℃. The Mn-Mg-Al-O catalysts were characterized by XRD. Their performance for NO_x oxidationstorage was investigated by adsorption measurements at constant temperature with or without SO₂ and the desorption of stored NO_x was also investigated by TPD under N₂. The results showed that Mn was well dispersed in the precursors. Mg₂MnO₄ was the major active component after calcinations. Mn was catalytically active for the oxidation of NO and exhibited certain NO_x storage capacity. Mg was the major component for NO_x storage; NO_x were stored with the formation of the nitrate that can be decomposed to NOx at 300℃~600℃ under N₂. The NO_x storage capacity was decreased by the presence of SO₂.