The deactivation of mesoporous silica-alumina (MSA) catalyst was investigated in the propene oligomerisation. Three catalysts with different acid site distribution were synthesised and tested, in order to determine the role of the acid sites in both main and side reactions. The initial activity is correlated with the Lewis acid site density. A two-stage mechanism for deactivation has been proposed. At the beginning of the reaction, poisoning of the active site takes place, the decay rate being consistent with the strength of the Lewis acid sites. At longer reaction time pore blockage, caused by an increasing of the dimensions of the adsorbed organic residues, becomes the main side phenomenon. (C) 2003 Elsevier Science B.V. All rights reserved.