The interdecadal variation of the relationship between ENSO and summer precipitation in China has been examined based on observed monthly rainfall data and NOAA ERSST data from 1951 to 2003. Results show that the relation has weakened during the past two decades, and the significance of ENSO as a predictor has also decreased. An evident example is that before the late 1970s, when above-normal (below-normal) SST appears over the Ni¿o-3 or Ni¿o-4 regions in previous winters, more (less) summer rainfall will often be found in North China and south of Yangtze River valley, less (more) rainfall appears along the Huaihe River valley, and the Chinese Meiyu will be later (earlier). However, all of these conclusions should be adopted carefully after the 1980s because of the feeble relation between ENSO and summer precipitation in China. This weakening relationship has increased the difficulty of summer rainfall prediction in China.