Abstract: Using monthly sea surface temperature from Hadley Center (HadISST) and the atmospheric reanalysis dataset provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) from 1979 to 2017, this study investigates the interdecadal variability characteristics of the relationship between El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) in boreal autumn and possible reasons behind. It is found that significant interdecadal variations exist in the ENSO-IOD relationship. Before the early 2000s, there was a significant positive correlation between them, and El Niño (La Niña) often corresponded to significant positive (negative) IOD events in the autumn. However, since the early 2000s, the ENSO-IOD relationship is significantly weakened and not statistically significant. Further studies indicate that the decadal change in ENSO spatial pattern plays an important role in the decadal change of their relationship. In the latter stage, the central Pacific El Niño events (CP El Niño) and eastern Pacific La Niña events (EP La Niña) occur more frequently, and the IOD intensity is more corelated with the longitudinal position than with the intensity of the CP El Niño. For the EP La Niña, the sea surface temperature anomaly (SSTA) is located more eastward than normal and over the cold tongue region of the equatorial Pacific. Under the effect of the cold climatic sea temperature, local atmospheric response is weak, and teleconnection effect over the Indian Ocean is weak, which results in a weak influence on the IOD intensity. Due to the combined effect of the CP El Niño and EP La Niña, the ENSO-IOD relationship is greatly weakened in the latter stage.