Effects of hydrochloride acid dealumination of mordenite (MOR) catalysts for the synthesis of 1-phenyl-1-xylyl ethane (PXE) were investigated. The structure and acidity of catalysts were characterized by XRD, BET, XRF, FT-IR, 27Al NMR and NH3-TPD techniques. The catalytic performance of the acid-treated MOR zeolites was studied through using the alkylation of o-xylene with styrene. The test results showed that the strength of remaining Br?nsted acid sites increased despite the reduction of total number of acid sites after dealumination, and the micropores of HMOR were slightly enlarged coupled with the formation of secondary mesopores. Additionally, the modiifed HMOR zeolites showed longer catalyst life with the styrene conversion rate retained. Among the catalysts employed in this study, the modiifed mordenite that was dealuminated by HCl (2 mol/L) could be used repeatedly without signiifcant loss of activity and selectivity during six cata-lytic runs, which have been ascribed to its speciifc acidity and structural properties.