In-situ observational works had been done for the investigation of Cochlodinium polykrikoides cell distributions and abundances off the coast of Busan, Jinhae Bay, and Namhae to Tongyong area in the early June, 2004. The surface water of 11 was concentrated by passing through ${Phi}$ 10 $mu extrm{m}$ mesh and cellular morphological characteristics of the species in the sample was observed under light microscope equipped with digital camera on the vessel. C. polykrikoides cells showed highest cell numbers ranging from 60 to 660 cells/1 at Jinhae Bay. Cell counts at offshore area of Busan ranged from 45 to 330 cells/1. However, no cell was found in the water between Namhae and Tongyong. C. polykrikoides found during the cruise had a large bright red and round cellular materials in one cell and two-celled chain of C. polykrikoides. The red material decreased as C. polykrikoides formed long chains through cell divisions.