The material discussed in this report was collected at 23 stations in the north of the continental shelf of the East China Sea from October 4 to November 5,1977 with a Juday phytoplankton net(diameter 37 cm,No.20 gauze) which was towed from the bottom to the surface of the sea.The Results anlayzed show that the species composition and distributon of dinoflagellates in this region bear a close realtionship to the water mass and the sea currents.Based on the temperature ranges in which different species of dinoflagellates flourish,they may be divided into three groups:cold-water species,warm-temperate species and warm-water species.The number of the last group is more than 70% of the total.