Through 1961-1973 more than 100 microbiological stations had been set up for studying the ecological distribution of heterotrophic bacteria in continental shelf of the East China Sea (28-32°N, 122-124°E). Samples were collected from bottom muds and sea waters in different depths. Heterotrophic bacterial population in sea water were counted by incubating the membrane filter on nutritional sea water medium.The number of heterotrophie bacterial colonies growing on the membrane filter ranged from several to hundreds per 40 ml sea water. The result of our investigation showed that the density of bacterial population in sea water samples collected from the area near the coast and estuary was generally higher, but the higher density of bacterial population had also been found in some samples collected from the area farther south,i.e. the open sea. It is interesting to note that these samples characterized by increasing bacterial population were regularly linked together and concentrated in some limited zones. In this case the distribution features of heterotrophic baeteria ean be used as an indicator for the dynamic distribution of some kinds of organic matter.According to the result of microbiological investigation, the hydrological structure in this area of East China Sea are more complieated than in the North. About 1300 strains of heterotrophic bacteria were isolated as pure cultures from the sea water and sediments. It was found that the biochemical reactions of these isolates are more active than that of isolates from open sea. All isolates were classified according to Bergey’s Manual of Determinative Bacteriology. Most of them belong to the genera: Pseudomonas, Vibrio, Aeromonas, Alcaligenes, Caulobacter, Flavobacterium,Micrococcus, Bacillus, Brevibacterium, Arthrobacter and Corynebacterium.We found that the Bacillus strains were the dominant bacteria and widely distributed in the sediments of continental shelf. It is our opinion that the Bacillus strains can be used as an indicating microorganism for studying the sediments of continental shelf.According to the result of our study we believe. that this investigated area of East China Sea has been under the serious influence of the continent.