The metallocene (nBuCp)(2)ZrCl2 was grafted on partially dehydroxilated commercial silica (Grace 948) whose surface had been chemically modified by wet impregnation of an oganosilane (Ph3SiCl, Me3SiCl, or Me2SiHCl) aiming at supported catalyst systems with well spaced alpha-olefin polymerization active centers. Final Zr loadings were determined by Rutherford Backscattering Spectrometry (RBS), and modifications at the silica surface after each preparation step were monitored by in situ FT-IR spectroscopy. These catalyst systems produced polyethylenes with narrow molecular weight distribution when methylaluminoxane was used as cocatalyst, with twice the activity of (nBuCp)(2)ZrCl2 supported on bare SiO2. Effects of support structure and chemical modification on catalyst performance are presented and discussed.