The performances of a non-noble metal (catalyst A), a non-noble metal catalyst containing a smaller amount of a noble metal (catalyst B) and noble metal (catalyst C) for NOx reduction at 400 - 600 degrees C and space velocity of 16X10(4)h(-1) have been studied by means of a fixed-bed continuous flow system. In both the absence and presence of oxygen, the following activity orders of catalysts for the reduction of NOx to N-2 by CO and C3H6(HC) can be given: C > B > A and B > A congruent to C, respectively. Meanwhile, there was CO formation in the reduction reactions of NOx by HC on the three catalysts. The amount of CO produced on catalyst C was the largest of the three catalysts.