Abstract: Zeolites have been extensively used in the chemical and petrochemical industries owing to their tunable acidities and unique pore structures. Beta zeolite with Brönsted and Lewis acids and AlCl₃@Si-Beta with only Lewis acid were prepared by hydrothermal synthesis and gas-phase impregnation methods, respectively. Mechanisms differences of Brönsted and Lewis acids on four pentene isomers transformation were investigated by in situ diffraction infrared Fourier transform spectrum (DRIFTS). The results suggested that Brönsted in Beta played a main role in isomerization and oligomerization reactions which all followed classical carbenium ion mechanisms. On the contrary, Lewis acid in AlCl₃@Si-Beta without hydrogen proton or hydroxyl catalyzed α-pentene double-bond migration to produce β-pentene and cis-trans isomerization reaction of 2-pentene by AB-AD mechanism with allyl-like species as intermediates, and could not catalyze pentenes skeletal isomerization and oligomerization reactions.