The Pacific-Japan (PJ) pattern is the dominant teleconnection over East Asia, closely related to the summer precipitation on various time scales. However, studies on the connection between the interdecadal variations of the PJ pattern and sea surface temperature (SST) forcing are still limited. This study indicates that the relationship between the PJ pattern and ENSO presents a pronounced interdecadal change around 1997/1998. The PJ pattern shows a baroclinic structure over the northwest Pacific and a barotropic structure near Japan during 1979-1997, while its baroclinic structure in the tropics weakens remarkably during 1998-2021, with a southward shift of its midlatitude barotropic structure. As a result, the connection between the PJ pattern and summer precipitation over East Asia exhibits an interdecadal transition in the late 1990s.