Early transition metal catalysts [N,N]MCln, in which [N,N] is N-(2,6-diisopropylphenyl)pyridine-2-carboxaldimine (C18H22N2, NN-1), N-(2,6-diisopropylphenyl)-6-methylpyridine-2-carboxaldimine (C19H24N2, NN-2), N-(2,4,6-trimethylphenyl)pyridine-2-carboxaldimine (C15H16 N2,NN-3), M is Ti, Zr and V, and n is 3 or 4, e.g. [NN-1]TiCl4 1a, [NN-1]ZrCl4 1b, [NN-1]VCl3 1c,[NN-2]TiCl4 2a, [NN-2]ZrCl4 2b, [NN-2]VCl3 2c, [NN-3]TiCl4 3a have been investigated to catalyze ethylene polymerization in the presence of methylaluminoxane (MAO). It was noteworthy that polyethylene characteristic of high molecular weight and wide or bimodal molecular weight distribution was formed with moderate to high activities.