The performance of ion-exchange resin catalysts during isobutene (IB) dimerization was investigated under different IB contents, temperatures and liquid-volume hourly space velocity (LHSV) using a plug flow reactor in the absence of any selectivity enhancing component. High IB content and temperature resulted in a high conversion and C12 selectivity but low C8 selectivity. The influence of LHSV was related with the IB content: LHSV had great effect at high IB content, while the performance of ion-exchange resin changed little with LHSV if IB content was low. The effect of water on the stability of resins was also studied. Desulfonation was observed during the C4 dimerization reaction when water was added to the feed. Chlorinated resin was more stable than conventional polystyrene-based resins during the test.