For the purpose to develop high active catalysts for low temperature reduction of NO with NH3, the effect of addition of halogenides (NH4Br, NH4I, NH4Cl, HBr) to Cu (II) -exchanged Y-type zeolite, V2Ox-activated carbon and V2Ox-TiO2 catalysts, etc. and the reduction mechanism were studied by the temperature programmed reaction and desorption methods. The experiments on the reduction of NO were carried out by using a flow re'actor (I.D.: 12.0 mm) under atmospheric pressure and at 90-220°C. The average diameter of the granular catalysts was 1.0 mm. Inlet gas concentration was mainly 470 ppmNO-30 ppmNO2-667 ppmNH3-5%O2-0 or 10%H2O-N2 and the total gas flow rate was 1000 Ncm3/min (space velocity: 4.0×104hr-1) toward 1.5 ml (bulk volume) of the catalysts. These results showed that NH4Br-Cu (II) -NaY was found to be highly active and stable catalyst. Furthermore, the reduction mechanism over Cu (II) -NaY and NH4Br-Cu (II) -NaY, the contribution of surface oxygen (= adsorbed oxygen+lattice oxygen) and adsorbed NH3 to the promotion of reaction rate was clarified.