Oil spill caused severe effects on the marine fauna and flora due to direct contact of organisms with the oil and even in regions not directly affected by the spill. This study was conducted to understand the effects of the oil spill accidents and the use of dispersant on the red tide of Cochlodinium polykrikoides. Crude oil produced in Kuwait, bunker-C, kerosene and diesel oil, and a chemical dispersant produced in Korea, were added with a series of 10 ppb to 100 ppm in the f/2-Si medium at 20℃ under a photon flux from cool white fluorescent tubes of 100 mol m-2 s-1 in a 14: 10 h L:D cycle for the culture of C. polykrikoides. In low concentrations of ≤1 ppm of examined oils no impact on the growth of C. polykrikoides was recorded, while in high concentration of ≥10 ppm, cell density was significantly decreased with the range of 10 to 80% in comparison with the control. The growth of C. polykrikoides after the addition of the dispersant and the mixtures combined with oils and a dispersant of ≥10 ppm appeared to decrease, whereas the growth of C. polykrikoides exposed to ≤100 ppb showed little serious impact. However, almost all the C. polykrikoides cells were died regardless of a dispersant and combined mixtures within a few days after the addition of high concentrations.