[1,8-C10H6(NR)(2)]TiCl2 [R = (SiPr3)-Pr-i (3a), (SiBuMe2)-Bu-t (3b), SiMe3 (3c)] complexes have been prepared from dilithio salts [1,8-C10H6(NR)(2)]Li-2 (2) and TiCl4 in diethyl ether in moderate yields (60-63%). These complexes could be identified by H-1 and C-13 NMR, mass spectroscopy, and elemental analysis. It turned out that these complexes exhibited high catalytic activities for ethylene homopolymerization and for ethylene/1-hexene copolymerization in the presence of methylaluminoxane (MAO), methyl isobutyl aluminoxane (MMAO), or (AlBu3)-Bu-i- or AlEt3-Ph3CB(C6F5)(4) as a cocatalyst. The effect of cocatalyst as well as solvent is very important for high activity, and it turned out that the catalytic activities performed in heptane (cocat. MMAO) were higher than those carried out in toluene (cocat. MAO). The catalytic ethylene/1-butene copolymerizations by the 3b-MMAO, (TBP)TiCl2-MAO [TBP = 2,2＇-thiobis(4-methyl-6-tert-butylphenolato)], or [Me2Si(C5Me4)((NBu)-Bu-t)]TiCl2-(AlBu3)-Bu-i/Ph3CB(C6F5)(4) catalyst system were also explored under the various conditions, and it was found that the l-butene contents and the triad sequence distributions of the resultant copolymer were highly dependent upon the catalyst used.