Communication: Ethylene was polymerized with cycloalkylidene-bridged cyclopentadienyl metallocene catalysts 1-9 in the presence of methyl aluminoxane (MAO) as the cocatalyst. Unlike the normal titanocene catalysts, the cycloalkylidene-bridged cyclopentadienyl titanocene catalysts show much higher activities than the corresponding zirconacene and halfocene catalysts and show the highest activities at higher temperature. This indicates that the cycloalkylidene-bridged cyclopentadienyl titanocene system is very thermally stable and maybe a very promising catalyst system for industrial application.