Alkylation of biphenyl with propylene was carried out over various zeolites such as HY, H-ZSM-5, Beta, MCM-22, SSZ-25 and SSZ-26. The influence of zeolite structure on reaction activity and selectivity was studied. The alkylation activity follows the order: Y > Beta approximate to SSZ-26 > MCM-22 > SSZ-25 > ZSM-5. The influence of framework Si/Al ratio and crystal size for the tri-directional 12 member ring structures (Y and Beta) has been studied and it has been observed that, under the reaction conditions used here, the process is not diffusion controlled. High selectivity to ortho-isopropylbiphenyl (o-IPBP) was obtained using MCM-22 and SSZ-25 zeolites, both with a MWW structure, The high o-IPBP selectivity as well as the differences observed between the two zeolite samples have been explained on the bases of differences in crystal size and assuming that on this zeolite structure the reaction only takes place on the external surface. (C)2000 Elsevier Science B.V. All rights reserved.