Selective synthesis of par-para'-dimethyidiphenylmethane (para-para'-DMDPM) from the condensation between toluene and formaldehyde was investigated over H-X, H-Y, H-ZSM-5, H-mordenite and MCM-41. Characterizations (NH3-TPD-MS and pore structure) disclosed that the catalytic activity of various zeolites depends mainly on its strong acid site and accessibility of the internal pores. H-beta zeolite, with a unique pore sized in 0.66 nm and higher proportion of stronger acid site, exhibited the highest activity and stereo-selectivity (86.5%). Small sized H-beta zeolite was more active due to the enhanced accessibility of its acid site, and this kind of zeolite remained a higher stereo-selectivity (> 80%) even at higher temperature, longer reaction time and recycle usage. The best yield of para-para'-DMDPM reached 71.1 % at 140 degrees C over H-beta zeolite and it could be used in recycle without loss of its structure, activity and stereo-selectivity. (C) 2007 Elsevier B.V. All rights reserved.