Two types of salicylaldiminato-based nickel complcxes, mono-ligated Ni (Ⅱ) complexes and bis-ligated Ni (Ⅱ) complexes were synthesized and characterized by FT-IR, NMR, MS and EA.In the presence of methylaluminoxane as cocatalyst, all the nickel complexes exhibited high activities for the polymerization of methyl methacrylate and syndiotactic-rich polymethyl methacrylate was obtained.The complexes with less bulky substituents on salicylaldiminato framework possessed higher activities, while with the same salicylaldiminato, the mono-ligated nickel complexes showed higher catalytic activity than bis-ligatcd ones.