The influence of acidity properties of zeolites on the alkylation of isobutane with 2-butene was studied using ultrastable Y (USY) zeolites. Most zeolites possessed almost comparable hydrogen transfer activity except for USY-30, which has the lowest acid site density. On the other hand, the strength of acid sites increased with degrees of dealumination. During the alkylation, a maximum in catalytic activity for certain Si/Al ratios were observed. This behavior is believed to be a result of a balanced level of acidic properties between the concentration and strength of Bronsted acid sites. It can prohibit the formation of heavy carbonaceous materials that deactivate the zeolites.