A series of aryl-substituted tetramethylcyclopentadienyl zirconocenes (C5Me4C6H4X-4)Cp'MCl2 [Cp' = C5H5, X = H (5), Me (6). Cl (7) or OMe (8); Cp' = Ind, X = H (9) Me (10) or Cl (11); Cp' = 2-Ph-Ind, X = H (12)] and (C5Me4C6H4X-4)(2)ZrCl2 [X = H (13), Me (14), Cl (15)], with different substituents at the 4-position of phenyl, have been prepared by the reaction of the corresponding ligands (C5Me4HC6H4X-4) [X = H (1), Me (2), Cl (3) or OMe (4)] with n-BuLi. ZrCl4 and Cp'Li or with n-BuLi and ZrCl4. Ethylene polymerization with these complexes in combination with MAO has been studied. The electron donor (Me) at the 4-position of phenyl led to an increase in catalytic activity while the electron-withdrawing group (Cl) and the strong pi donor (OMe) led to its decrease. Complexes 5, 6, 9 and 10 exhibited very high activities, but 13-15 showed much lower activities due to the bulky steric effect. The molecular structure of 5 has been determined by X-ray diffraction. The relationship between structures of catalysts and catalytic activities were discussed. (C) 2002 Elsevier Science B.V. All rights reserved.