Aluminas thermally and/or chemically treated were used as support for Cp2ZrCl2 and evaluated in ethylene polymerization at constant reaction conditions. Two different calcination temperatures were employed, and the metallocene was fixed either directly or after support pretreatment with MAO, TAM, or NaOH solutions. The obtained alumina-supported catalysts showed activities comparable to the homogeneous precursor. It was noticed that the textural properties of the supports strongly influenced the catalyst performance. The direct fixation of the metallocene on alumina produced catalysts presenting lower activities in comparison to the ones obtained from the chemically treated supports. The chemical pretreatment of hydrated alumina with TMA originated catalysts whose activities were superior to those obtained by pretreatment with MAO. The pretreatment with NaOH produced the more active catalyst and generated branched polymer. The molecular weight of the PE produced by the supported catalysts was higher than the ones obtained with the homogeneous system. (C) 2003 Wiley Periodicals, Inc.