Reaction kinetics for selective catalytic reduction (SCR) of nitric oxide (NO) over 1% Pt/MCM-41 catalyst has been investigated at temperatures ranging 150-500 degreesC under steady and transient state conditions. The reduction of NO is found to be promoted by a small amount of oxygen when the concentration of oxygen is less than that of the critical oxygen concentration required for stoichiometric oxidation of C3H6. Above the critical oxygen concentration, an optimal reaction temperature for optimal NO conversion is observed and the optimal NO conversion decreases with the increase of oxygen concentration. Two distinct kinetic regions are observed: one at the reaction temperature below and the other one above that required for optimal NO conversion. The NO reduction rate is suggested to be controlled by the activation rate of C3H6 at low temperatures and by the external diffusion rate of reactants at high temperatures.