The ethylene/styrene copolymerization by Cp*TiCl2(NdCtBu(2)) (Cp* = C5Me5, 1) - methylaluminoxane (MAO) catalyst proceeded in a living manner, and the living nature maintained under various conditions (Al/Ti molar ratios, ethylene pressure, styrene concentrations, temperature). Poly(ethylene-co-styrene)s were obtained exclusively in the polymerization using 1, Cp*TiX2(O-2,6-(Pr2C6H3)-Pr-i) [X = Cl (3), Me(5)] - MAO, and 5-[PhN(H)Me-2][B(C6F5)(4)] catalysts under the same conditions, and both the styrene incorporation and the microstructures were highly influenced by the anionic donor ligand employed. The resultant polymers prepared by Cp*TiX3 [X = Cl (4), Me (6)] - MAO catalysts were a mixture of polyethylene and syndiotactic polystyrene (SPS), whereas the resultant polymer did not contain SPS in the polymerization by 6-[PhN(H)Me-2][B(C6F5)(4)] catalyst. These facts clearly indicate that the anionic donor ligand strongly affects the styrene incorporation and the polymerization behavior and that catalytically active species for the syndiospecific styrene polymerization and the copolymerization are apparently different.