A series of nickel complexes ligated by 2-(2-benzimidazole)-6-methylpyridine, 2-(1-methyl-2-benzimidazole)-6-acetylpyridine, and 2-(1-methyl-2-benzimidazole)-6-(1-aryliminoethyl)pyridine was synthesized and examined by IR spectroscopic and elemental analysis. Their molecular structures were determined by single-crystal X-ray diffraction analysis. On activation with diethylaluminum chloride (Et2AlCl), all the nickel complexes exhibited good catalytic activities for ethylene oligomerization, and the nickel(II) complexes bearing 2-(1-methyl-2-benzimidazole)-6-(1-aryliminoethyl)pyridines showed good activities up to 5.87 × 105 g mol-1(Ni) h-1 atm-1. The various reaction parameters were investigated in detail, and the results revealed that both the steric and electronic effects of ligands strongly affect the catalytic activities of their nickel complexes as well as different coordination style.