Investigations on distribution patterns and variation of dissolved oxygen (DO) were carried out around the Changjiang River Estuary in August and November of 1985 and in January and May of 1986. The results showed that there was a significant negative correlation between DO and temperature in autumn and winter. DO was supersaturated in spring and summer due to high content of phytoplankton with average oxygen saturabilities of 105% and 112%, separately. The maximum value of DO (15.32mg O2/L)was found in the middle part of the area during summer with oxygen saturability of 221%, phytoplankton content of 7.82×107 cells/m3, and chlorophyl-a concentration of 38.3 mg/m3, correspondingly.