The behaviour of mesoporous silica as a support for anchored catalytic species depends on its physical and chemical surface properties, particularly those related with the hydroxyl groups. In this report, the number and nature of hydroxyl groups of a commercial silica sample calcined at different temperatures have been determined by titration with triethylaluminium and IR, respectively. The preparation of supported metallocene catalyst has been studied by different ways. The calcination temperature affects deeply the ability of the support to anchor the different species involved in this catalytic system. The polymerization reactions carried out using silica and MAO/silica supports show how the chemistry of the silica surface plays a determinant role in the immobilization of this catalytic system.