This study investigates the interdecadal variation in the impact of the El Niño-Southern Oscillation (ENSO) on the East Asian upper-tropospheric westerly jet (EAJ) and the associated tropospheric temperature changes. The results identify a significant weakening of ENSO's influence on the summer EAJ after the early 2000s. This interdecadal shift mainly appears in June and closely linked to alterations in the rate of ENSO decay. After the early 2000s, a faster decayed ENSO leads to a weaker tropical tropospheric temperature, with a weakened meridional temperature gradient, results in a weaker westerly flow in the subtropics south of the westerly jet stream. This shift has important implications for climate prediction in East Asia.