A highly efficient CeOx-BC0.6 (BC: biochar. 0.6: mass ratio of Ce/(BC + Ce)) catalyst was prepared by air oxidation for low temperature NH3 selective catalytic reduction of NOx. The catalytic performance, character-ization and reaction mechanism of the CeOx-BC0.6 were investigated. The results showed that NOx conversion and N2 selectivity of CeOx-BC0.6 catalyst obtained by calcining in air were above 90 % at 150-300 degrees C and 100,000 h-1. The surface oxygen groups, acid sites and oxygen vacancies were generated by air oxidation treatment, which promoted the adsorption and activation of reactants. NH3 and NOx were adsorbed on the catalyst surface in the form of NH4+, NH3+, nitrite and nitrate adspecies. The redox cycles of ketonic carbonyl/ phenol (C–O/C-OH) pairs and Ce4+/Ce3+ pairs were responsible for the activation of NH3 and NOx. NH2NO and NH4NO2 were the main active intermediates. The reaction of NH3 selective catalytic reduction of NOx over CeOx- BC0.6 mainly followed Eley-Rideal mechanism. These results will promote the understanding of mechanism of NH3 selective catalytic reduction of NOx for biochar-based catalyst prepared by air oxidation.