In the work reported in this article, 1-pentene reactions were carried out over USHY zeolite, whose strong-acid sites were selectively poisoned by hard coke to study the role of these strong zeolitic acid sites on hydrocarbon conversions. We show conclusively that strong-acid sites are responsible for cracking and hydride transfer reactions as well as strong coke formation, whereas weak-acid sites can only catalyze double-bond isomerization.