Ethylene was selectively oligomerized by nickel complexes such as (PPh3)2NiBr2 and (PPh3)2NiCl2 immobilized in chloroaluminate ionic liquid in biphasic catalytic reactions. The influence of reaction parameters such as reaction media, reaction temperature and Et2AlCl:Ni molar ratio was also evaluated. Turnover frequency up to 24000 mol C2H4/(mol Ni h) was achieved under mild reaction conditions (0.5 atm and 40 °C). GC‐MS analyses showed that the obtained oligomers completely consist of C4 and C6. The olefinic products can be easily separated from the catalytic ionic liquid phase by simple decantation, and the nickel catalyst can be reused without a significant decrease in turnover frequency and change of the distribution of the olefinic products. Copyright © 2009 John Wiley & Sons, Ltd. Ethylene was selectively oligomerized by (PPh3)2NiBr2 and (PPh3)2NiCl2 immobilized in chloroaluminate ionic liquid in biphasic catalytic reactions to produce C4 and C6. The olefinic products can be easily separated from the catalytic ionic liquid phase, and the ionic liquid phase containing the catalyst can be recycled and reused at least three times without much change in the activity and oligomer distribution.