The surface wind anomalies associated with the Madden-Julian oscillation (MJO) appear to play a critical role during the onset and termination phases of ENSO. The characteristics of the MJO-related oceanic Kelvin waves have not been systematically studied due to a lack of ocean reanalysis that resolves intraseasonal variability. This study uses the operational ocean reanalysis for the period 1982–2003 produced by the state-of-art global ocean data assimilation system at NCEP to explore the relationship between SST anomalies of ENSO and MJO-related oceanic Kelvin waves. The first four extended empirical orthogonal functions of the depth of 20°C isotherm are used to represent the dominant oceanic Kelvin waves. The wave activity is measured by seasonal variance of oceanic Kelvin waves (SVKW) at 130°W. SVKW peaks are associated with the onset stage of warm ENSO events since they occur during the transition period and tend to produce positive tendency in NINO3.4 and heat content, and lead mature phases by 5–11 months. MJO-related oceanic Kelvin wave activity is also shown to impact the growth and termination of warm events. The consistent relationships do not occur in cold events. A real time monitoring tool using SVKW index is proposed to support the official ENSO forecast at NCEP.