New CrAlSBA-15 mesoporous materials have been prepared by direct synthesis and characterized by ICP-AES, XRD, N-2 adsorption, Al-27 NMR, TEM, UV-vis and H-2-TPR. CrAlSBA-15 materials exhibited high mesostructural order starting from chromium(III) nitrate (Si/Cr=66; Si/Al=35 at pH 3) and from chromiurn(III) acetate hydroxide (Si/Cr=39; Si/Al=51 at pH 1.5). The incorporation of chromium and aluminium into SBA-15 mesoporous structure is enhanced by increasing the pH and produces an increase in pore size and pore volume. After calcination, samples prepared by one-step synthesis showed Cr(VI) centres well dispersed with a proportion of chromate species higher than Cr/AlSBA-15 catalysts prepared by impregnation and grafting. H-2-TPR measurements showed that only the 80% of Cr(VI) ions incorporated into the SBA-15 structure were reduced, so part of chromium ions may be located in non-accessible positions inside the solid walls. CrAlSBA-15 materials obtained by direct synthesis exhibited higher ethylene polymerization activity (381.1 kg PE/g Cr h) than Cr/AlSBA-15 and conventional Cr/SiO2 Phillips catalyst prepared by impregnation (260.5 and 216 kg PE/g Cr h, respectively). (C) 2007 Elsevier B.V. All rights reserved.