The hydrographic structure and offshore extension of freshwater plume discharged from the Changjiang (also known as the Yangtze) River in the northern East China Sea were investigated by analyzing conductivity-temperature-depth (CTD) data and drifter trajectories collected during the summers of 1997 and 1998. From June to early September, when southerly winds prevail, the plume tends to move northeast in the Chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern East China Sea. During other seasons, when northerly winds prevail, the plume is confined to the Chinese coast. In the summer the plume in the midshelf, confined to a thin surface layer 10 to 15 m thick, extends eastward in the form of patches of low-salinity water rather than spreading as a tongue-shaped pattern from the Changjiang mouth. The eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds. Upon reaching the vicinity of Cheju-do, an island in the middle of northern East China Sea, the patches are advected to the Korea/Tsushima Strait by either the Cheju Warm Current or a northward-flowing mean current of the Kuroshio Branch Current and then finally flow into the East/Japan Sea.