Ethylene–norbornene (E–N) copolymerizations were carried out by using β-diketiminato nickel complexes CH{C(CF3)NAr}2NiBr (Ar=2,6-iPr2C6H3, 1; Ar=2,6-Me2C6H3, 2) in the presence of methylaluminoxane (MAO). Complex 1 bearing bulky isopropyl ortho substituents showed higher activity than 2 for the E–N copolymerization. The activity of the catalytic systems increased with increasing the feed ratio of norbornene/ethylene (N/E), and gave the E–N copolymers with high norbornene content more than 75mol%. In the microstructures of copolymers generated with the catalytic systems, norbornene microblocks with a length of two or three norbornene units have been detected. Results have shown that the activity and the content of norbornene in copolymer depend on the N/E feed ratio.