The effect of amount and strength of acid sites on the activity and selectivity for the selective reduction of NO with C3H6 in the presence of excess oxygen over H-form and ion-exchanged zeolites has been investigated. The activity was found to be proportional to the acid amount determined by NH3-temperature programmed desorption, but independent of the acid strength of the zeolites. The selectivity, i.e., the ratio of the reduction of NO with C3H6 to the oxidation of C3H6 by O-2, was independent of the amount and strength of acid sites.