Abstract: In the past decade, the Prorocentrum bloom was the most frequently occurred bloom in the East China Sea. It occurred every one year or two years, and covered huge areas. There were arguments on the identification of Prorocentrum bloom causative species. Some scientists thought the species being P. dentatum Stein, but the others thought that it was a new species, P. donghaiense Lu. For achieving the proper classification of the species, an "International Workshop on HAB Causative Species-Taxonomic View on a species of Prorocentrum in the East China Sea" was held in Shenzhen, China in November, 2002. By reviewing as much as available references, and by comparing the Prorocentrum specimen from the East China Sea with those from Japan, Korea and USA, scientists participated in this Workshop agreed that: 1) the specimens from Japanese and Korean waters, and from CCMP, USA were the same species; 2) the features of anterior projection and cell surface marking were similar to those of originally described P. dentatum Stein; 3) the major difference is the cell size. The specimens from the East China Sea were mostly less than20 μm long, whereas the size of the original described P. deatatum was larger than 50 μm; 4) the minor difference is the shape of the cell end. The original described P. deatatum was with a pointed end, whereas the cells from the East China Sea were mostly with a rounded end. There was no final agreement for the species identification at the Workshop. By summing all views of scientists from the Workshop, the authors suggested that the bloom causative species of Prorocentrum in the East China Sea, as well as so-called species of P. dentatum from other East Asian waters, should be the same species. They are all P. donghaiense Lu.