Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 and 100 were synthesised and characterised by XRD, FT-IR, Al-27-MAS NMR and BET techniques. Their catalytic activity in the esterification of acetic acid with amyl alcohol was studied in the vapour phase between 150 and 250degreesC. The activity of the catalysts followed the order Al-MCM-41 (100) >Al-MCM-41 (75) > Al-MCM-41 (50) > Al-MCM-41 (25). The study of time on stream at 250degreesC showed about 25% decrease in conversion at the end of 5 h. The influence of feed rate and feed ratio on conversion was also studied and the results are discussed. (C) 2004 Elsevier B.V. All rights reserved.