Ethylene copolyrnerizations with 4-methylcyclohexene (4-MeCHE) or 1-methylcyclopentene (1-MeCPE) have been explored by the aryloxo- or ketimide-modified half-titanocenes, Cp'TiCl2(X) [X:O-2,6-'Pr2C6H3; Cp':1,2,4-Me3C5H2 (1), (BuC5H4)-Bu-t (2), C5Me5 (Cp*); X:N=(CBu2)-Bu-t; Cp':(BuC5H4)-Bu-t, Cp, indenyl], linked half-titanocenes, [Me2Si(C5Me4)(NR)]TiCl2 (R = Bu-t, cyclohexyl), and ordinary metallocenes, [Et(indenyl)(2)]ZrCl2, Cp2ZrCl2, in the presence of methylaluminoxane (MAO) cocatalyst. The aryloxo analogues (1, 2) showed rather efficient 4-MeCHE incorporations in-a 1,2- (or 2,1-) insertion manner, affording the copolymers with unimodal molecular weight distributions (as well as with uniform compositions observed as single melting temperature by the DSC thermograms), whereas to the others they showed negligible incorporations under the same conditions. Only the 1,2,4-Me3C5H2-aryloxo analogue (1) afforded the copolymers containing 1-MeCPE with uniform, compositions, and 1-MeCPE was incorporated with 1,2-insertion as well as after isomerization (1,3-insertion, incorporated as methylene cyclopentane units), whereas incorporation of 1-methylcyclohexene (1-MeCHE) was rather negligible.