A series of new nickel(II)complexes with 2-aminomethylpyridine igands.(2-PyCH2NHAr)2,NiBr2(Ar=2.6-dimethylphenyl 2a;2,6-diisopropylphenyl 2b,2,6-difluorophenyl 2c),have been synthesized and used as catalyst precursors for ethylene polymerization in the presence of methylaluminoxane (MAO).The catalysts containing ortho-alkyl-substituents afford high molecular weight branched polyethylenes as well as a certain amount of oligomers.Enhancing the steric bulk of the alkyl substituent of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer.Catalyst 2c containing ortho-fluoro-substituents exhibited the highest catalytic activity.but only oligomers in which C12H24 had the maximum content were obtained by the catalyst.The molecular weight,molecular weight distribution,and microstructure of the resulted polymer were characterized by gel permeation chromatography and 13C-NMR spectrogram.