Abstract: The relationship between ENSO and Indian Ocean Dipole is discussed in this paper by using the data set of sea temperature from Scripps Institute of Oceanography, the air temperature at 1000hPa from the NCEP reanalysis data and the NINO3 index from the Climate Prediction Center (CPC) of U.S.A. during the period from 1955 to 2001. The results show that there exists a Dipole on the maximum anomalous temperature level (MATL) in the Indian Ocean, which close relates to ENSO in the Pacific Ocean. During El Nino periods there are good relationships between ENSO and Indian Ocean Dipole with the maximum correlation occurring when the ENSO leads by one month, but in La Nino periods the relationship is not so good. The distribution of Dipole in Indian Ocean is from northeast to southwest, with one (west) pole in 65oE-75oE，6oS-10oS and the other in 85oE-95oE，2o-6oN, which is different from that defined by Saij. The correlation coefficients of NINO3 index with temperature anomalies in the west/east poles on the MATL are over 0.4/-0.15, respectively. It is a main sea temperature system in the tropical Indian Ocean. However, in the surface layer from sea surface to 20-30 m depth there is no such a dipole with opposite sea temperature anomalies in the NE and SW of tropical Indian Ocean. The SSTA in the NE might be influenced by the sensible exchange process because the evolution of sea and 1000hPa air temperature anomaly time series of the NE of tropical Indian Ocean is quite similar except 1962-1963 and 1986. The periods of the Indian Ocean Dipole are shorter than that of ENSO, and about 1 to 6-year.