In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxane-diylbis(cyclopentadienylindenylzirconium dichloride) (3) and hexamethyltrisiloxanediyl-bis(cyclopentadienylindenylzirconium dichloride) (4) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopenta-dienyldimethylzirconium (1). On the other hand, weight-average molecular weight <(M)over bar (w)> and ratio of weight- to number-average molecular weights <(M)over bar (w)>/<(M)over bar (n)> of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4, it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. <(M)over bar (w)>/<(M)over bar (n)> of PE could be adjusted by changing the relative concentrations of the two zirconocenes.