The Keggin phosphotungstic acid, H3PW12O40 (HPW), was successfully immobilized on the surface of mesostructured LaSBA-15 by means of chemical bonding to aminosilane groups. The catalysts were characterized by elemental analysis, N-2 adsoption, TEM, DRS-UV, and FTIR spectroscopy. Characterization results suggest that the surface area decreased after grafting amino groups to silica and the structures of heteropolyanions on amine-modified LaSBA-15 was maintained. Their catalytic behaviors were investigated in the alkylation of o-xylene with styrene. Among the functionalized catalysts, when the content of amino-groups was suitable, it had the best catalytic performances in terms of yield and stability. It is worth mentioning that the catalysts could be used repeatedly without loss of the activity and selectivity during several catalytic cycles. The good stability can be attributed to the strong interaction between the amino groups on the surface of LaSBA-15 and HPW anions. The Keggin phosphotungstic acid, H3PW12O40 (HPW), was successfully immobilized on the surface of mesostructured LaSBA-15 by means of chemical bonding to aminosilane groups. The obtained catalysts were highly effective for alkylation of o-xylene with styrene in terms of yield and stability. Compared with the HPW/LaSBA-15 catalyst, both the catalytic stability and reusability were greatly enhanced.