NOx and particulate matter are the main environmental hazards in the diesel exhaust. In order to explore a suitable method to remove NOx as well as particulate matter, we have examined the catalytic reduction of NOx with soot in the presence of oxygen. Pt catalyst loaded on Al2O3-coated honeycomb was found to be more active than K, Ca and Cu catalysts. Even in the presence of 8% O-2, NO can be reduced to N-2 by soot with Pt catalyst. NO was completely converted to N-2 in the isothermal reaction at 500 degrees C, and the high activity of the catalyst retained for a long time period. The effects of Pt catalyst and O-2 on the mechanism of C-NO reaction was examined by using step response experiment.