Al-MCM-41 (Si/Al = 52 and 105) and Al-MCM-48 (Si/Al = 47 and 102) molecular sieves were synthesised by hydrothermal method. These materials and commercial HY zeolite were characterised by XRD, BET, 27 Al MAS-N MR, pyridine adsorbed FT-IR and ICP-AES techniques. The vapour phase cyclohexylation of ethylbenzene (EB) with cyclohexene was carried out between 200 and 400 degrees C over all the catalysts. The major products were found to be p-cyclohexyl ethylbenzene (p-CEB) and o-cyclohexyl ethylbenzene (o-CEB). The activity of the catalysts followed the order Al-MCM-41 (52) > Al-MCM-41 (105) > Al-MCM-48 (47) > Al-MCM-48 (102) > HY. Al-MCM-41 and Al-MCM-48 are more active than HY although the density of acid sites of the former catalysts is less than the latter. This is due to the large pore size of Al-MCM-41 and Al-MCM-48 catalysts that permits simultaneous entry of more reactants into the pores and expulsion of products freely out of the pores. Al-MCM-41 catalysts are more active than Al-MCM-48 catalysts due to more density of acid sites on the channel surface of Al-MCM-41. The selectivity of p-CEB is higher than o-CEB due to less steric hindrance for its formation. The effects of feed ratio and WHSV on ethylbenzene conversion and product selectivities were evaluated in the above reaction. (C) 2007 Elsevier B.V. All rights reserved.