The effect of the Indian Ocean on El Ni¿o/La Ni¿a life cycles has been studied using 200-yrs simulation data of a coupled GCM. The results show that the interactive feedback between the ENSO and the Indian Ocean holds the key to the rapid transition to an opposite phase. This remote impact of the Indian Ocean SST anomaly is linked to the change of zonal wind stress in the western Pacific, which leads to a rapid demise of El Nino/La Nina. Without the involvement of the Indian Ocean, the phase transition is much slower. This role of the ENSO--Indian Ocean coupling on ENSO transition is consistent with that derived from the observational analysis.