A series of different steric hindrance nickel(II) complexes 1-6 bearing 2,6-bis(imino)pyridine ligands have been synthesized and characterized. The molecular structures of the complexes 3-5 were determined by X-ray diffraction analysis. The coordination geometry around the nickel center of the complexes is either square pyramid for complexes 3 and 4 or trigonal bipyramid for complex 5. All of the nickel complexes exhibit high catalytic activity for norbornene polymerization in the presence of MAO, although low activity for ethylene oligomerization and polymerization. The effects of the Al/Ni ratio, halogen, monomer concentration, temperature, and reaction time on activity of catalyst for norbornene polymerization and polymer microstructure were investigated. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1486-1495, 2009