The novel chloro(1-naphthyl)[8-(diphenylphosphino)quinoline]nickel(II) (1), chloro(1-naphthyl)[2-methyl-8-(diphenylphosphino)quinoline]nickel(II) (2), and [2-methyl-8-(diphenylphosphino)quinoline]nickel(II) dichloride (3) complexes were synthesized in satisfactory yield and fully characterized. The structures of complexes 1 and 3 were determined by single crystal X-ray analysis, which indicated that complex 1 exists in a square planar configuration, while complex 3 is dimeric square pyramidal. In the presence of MAO cocatalyst, complexes 1–3 displayed good catalytic activities for ethylene oligomerization in toluene, up to 2.45 × 10⁵ g ethylene (mol Ni·h·atm)⁻¹ by complex 3.