Ethylene-norbornene (E-N) terpolymerization experiments using the linear olefin I-octene (O) or the alicyclic vinylcyclohexane (VCH) were conducted with two different ansa-metallocene compounds Zr(eta(5):eta(5)-C5H4CPh2C13H8)C-12] (1) and [Zr{(eta(5)-2,5-Me2C5H2)(2)CHMe}Cl-2] (2). The terpolymers obtained were investigated in detail by determining microstructure and termonomer contents by C-13 NMR, molar masses, and thermal properties. Chain end group analysis gave insight into factors that influence termonomer insertion and chain termination. Terpolymer molar masses were lower than those of the corresponding copolymers, those from 1 being higher than those from 2. This is related to the lower tendency of catalyst 1 to give beta-H elimination at a last enchained E unit as revealed from the low amount of vinyl chain end groups in H-1 NMR spectra. In VCH terpolymers from catalyst 1, only vinylene end groups, arising from 2,1 VCH insertions after one last inserted E unit, are present. This along with the lower activity reveals that VCH insertion is more difficult with this catalyst than with catalyst 2. Furthermore, all experiments showed that in general VCH is more difficult to coordinate to an active catalyst than O. While catalyst 1 provides higher molar masses, catalyst 2 enables to reach higher activities, higher N and termonomer contents, and higher T-g values. Finally, it was found that termonomer content greater than 3 mol % clearly affects T-g values. Thus, preparation of norbornene-ethylene-alpha-olefin terpolymers with high T-g and attractive molar masses was achieved in high yield by metallocene catalysts.