The spherical magnesium chloride (MgCl2)-supported methylaluminoxane (MAO) pre-catalysts were prepared using MgCl(2)(.)2.6EtOH adduct as support material subjected to elimination of EtOH by thermal treatments. The pre-catalysts were characterized by X-ray diffraction (XRD), IR, Al-27 solid-state NMR, scanning electron microscopy (SEM) and N-2 BET surface areas. Under the activation of triethylaluminum (TEA), polymerization of ethylene were carried out by contacting supported MAO with soluble dichloro(rac-ethylene-bis(1-indenyI))zirconium (rac-Et(Ind)(2)ZrCl2) prior to polymerization. As a result, the polymers with spherical form morphology and high bulk density (over 0.35 g/cm(3)) were obtained. The addition of cross-linking agents (CAs) during the adsorption of MAO on the support (e.g. glycol, glycerol and triethanolamine) led to an increase in Al content from 3.8 to 9-12 wt.% and in the catalyst activity, The highest activity in ethylene polymerization (3.48 x 10(7) g polyethylene (PE)/(mol Zrh)) was achieved in the case of using glycerol as CA. (C) 2002 Elsevier Science B.V. All rights reserved.