A series of supported catalysts were prepared by combining (nBuCP)(2)ZrCl2 and Cp2ZrCl2 sequentially grafted on silica in different ratio (1: 1 and 1:3) and immobilization order. Catalyst systems were characterized by Rutherford backscattering spectrometry (RBS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Grafted metal content remained comprised between 0.37 and 0.53 wt.% Zr/SiO2. All the systems were shown to be active in ethylene homopolymerization having methylaluminoxane as co-catalyst. Catalyst activity was shown to be dependent on the metallocene nature, but not on the addition order or molar ratio. The highest activity was achieved with CP2ZrCl2/(nBuCp)(2)ZrCl2 (1:3) catalyst system (ca. 4.26 kg PE (mmol Zr h)(-1)). Resulting polymers were characterized by GPC and DSC. In spite of bearing two catalyst centers, no bimodality was observed in the resulting polymers. (C) 2003 Elsevier B.V. All rights reserved.