A series of methylaluminoxane (MAO)-modified silicas were prepared by the impregnation method, using MAO toluene solution with concentration ranging from 0.0 to 20.0 wt.% Al/SiO2. The resulting solids were characterized by complementary spectroscopic and volumetric techniques, namely, inductively-coupled plasma-optical emission spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-VIS), X-ray photoelectron spectroscopy (XPS), diffuse-reflectance (DRIFTS) infrared spectroscopy, scanning electron microscopy (SEM) analysis and electron probe microanalysis (EPMA). Resulting texture of the modified silicas were analyzed by nitrogen sorption based on the Brunauer-Emmett-Teller (BET) method. Surface saturation seems to take place at about 10 wt.% Al/SiO2, based on the consumption of silanol groups, which were monitored by DRIFTS. XPS Al 2p spectra indicate the generation of two surface species for Aluminum content higher than 10wt.% Al/SiO2. Considering the presence of trimethylaluminum (TMA) in commercial MAO, it is very likely that depending upon the Al concentration, a competitive reaction for the immobilization sites (silanol groups) might take place, specially due to the higher reactivity and less steric effect played by TMA, therefore, generating different Al species. (C) 2002 Eisevier Science B.V. All rights reserved.