A new type of half-metallocene catalyst for the polymerization of ethylene and styrene Cp * M((O) 3 O 9 Si 7 (c-C 5 H 9 ) 7 ) (M= Ti (1), Zr (2)) is prepared by the reaction of (HO) 3 O 9 Si 7 (c-C 5 H 9 ) 7 with Cp * MCl 3 in the presence of triethylamine. Complex 1 is stable to heat and air but heavier congener 2 is sligtly air sensitive. The catalytic systems 1/MMAO and 2/MMAO, in which MMAO is modified methylaluminoxane show good activities in ethylene polymerization, with that of 2/MMAO greater than that of 1/MMAO. Polyethylenes with bimodal molecular weight distributions were obtained. In addition, the catalytic system 1/MMAO shows fairly good activities for the syndiospecific polymerization of styrene.