Zeolite H-ZSM-5 was used as support for the impregnation Of Cp2ZrCl2 catalyst in the synthesis of polyethylene. The catalyst preparation conditions were varied and the statistic program was employed with the purpose of evaluating the best catalyst preparation method. In order to utilize zeolite as support material it was necessary to perform a thermal treatment, which is composed by a pre-drying at 120 degreesC and afterwards a calcination at 300 degreesC under heating rate of 2 degreesC/min before treatment with methylaluminoxane (MAO) and bis(cyclopentadienyl) zirconium dichloride. It was observed that high amounts of zirconium fixed on the support surface did not lead to catalysts with higher activities, but in general the molecular weights of the obtained polyethylenes were very high. Furthermore, the supported catalyst was submitted to a longer MAO pre-contact before starting the polymerization by feeding the monomer, causing a sharp increase in the catalyst activity. (C) 2002 Elsevier Science B.V. All rights reserved.