Abstract: Based on field observations during1997 to 1999,the distributions of micronutrients and their limitation on the growth of phytoplankton in the Yellow Sea and the East China Sea were discussed in this paper. The results showed that there were abundant nutrients in the area of the east and northern-east of the Changjiang River estuary, and the nutrients came from the extension of the Changjiang River diluted water and the transportation of the Subei Coastal water. Besides, the maximum extension range of the nutrients in the Changjiang River diluted water was observed during the catastrophic flooding period of the Changjiang River in the summer of 1998. Based on the Redfield ratio (Si:N:P=16:16:1) in which,three essential nutrients were utilized by marine phytoplankton, the Si/N/P ratios were calculated and studied for the upper water of the Yellow Sea and the East China Sea. The results indicated that Si/N ratios were very high, which suggested that silicate was not the limiting factor for the growth of phytoplankton in the Yellow Sea and the East China Sea. However, under the influence of terrestrial runoff, especially the Changjiang River runoff which was rich in combined nitrogen and had very high N/P ratios, high N/P ratios occured in the Changjiang River estuary and its adjacent areas such as the south and southwest of the Yellow Sea, the inshore area of the East China Sea and the area east of the Changjiang River estuary in spring and summer. As a result, in contrast to general open marine systems, the systems in these areas resembled estuarine ones rather than typical marine ones. The primary production in a considerable portion of the Yellow Sea and the East China Sea might be limited by phosphate rather than nitrogen.