Esterification of terephthalic acid with methanol was carried out over Al-MCM-41 (Si/Al = 25, 507 75 and 100) molecular sieves in the vapour phase (with respect to methanol) at 200, 250, 300 and 350 degrees C, and under autogenous pressure conditions at 200 degrees C. The vapour phase reaction showed 90% conversion at 300 degrees C over Al-MCM-41 (100) with 100% selectivity to dimethyl terephthalate (DMT). Under the autogenous pressure, the reaction yielded about 95% DMT over Al-MCM-41 (100). The catalytic role of Al-MCM-41 was established by comparing activity with Si-MCM-41. The effects of various reaction parameters such as temperature, terephthalic acid loading, methanol flow rate, and catalyst weight on conversion were studied and the results discussed. (c) 2005 Published by Elsevier B.V.