Abstract: Differences of characteristics of ENSO variability between two different climatological background states were investigated by means of two numerical experiments with a coupled ocean-atmosphere general circulation model. The analyses concerning interannual variabilities of the sea surface temperature, upper ocean heat content,and surface wind anomalies, as well as the relationship between these three variables and the eastern equatorial Pacific sea surface temperature anomaly, exhibit distinguishing processes of the ENSO cycle for different background states. It was found that the ENSO characters including the frequency and the amplitude and its controlling mechanism strongly depend on the climatological background states. Two different ENSO modes were identified for the two different background states. One is the "delayed oscillator" mode, corresponding to a background state close to the observation; and the other is a stationary mode, corresponding to a background state with a decreased zonal thermal gradient and a flat thermocline structure along the equatorial Pacific. Resups presented in this study provide a clue to further understand the role of interdecadal variabilities played as a background state in the interannual variability of ENSO.