Nickel ion-exchanged MCM-36 and MCM-22 zeolites were prepared, characterized, and tested in the ethylene oligomerization reaction performed in slurry semi-batch mode (T = 70-150 degrees C, p = 4 MPa). The behavior of catalysts was evaluated in relation to their texture and nickel cations/acid sites ratio. NiMCM-36 catalysts, with large accessibility in the mesoporous structure and mild acidity, showed an excellent activity (46 g of oligomerS/g(catalyst) h) and selectivity (100% olefins with even number of carbon atoms) in ethylene oligomerization, while lower catalytic activity and selectivity were observed over NiMCM-22 possessing microporous structure and high acid sites concentration. (c) 2007 Elsevier B.V. All rights reserved.