The effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides Margelef isolated from the South Sea of Korea were examined in the laboratory. Growth was examined under the following combinations of temperature and salinity: 15, 20, 25 and $30^{circ}C$, and 15, 20, 25, 30 and 35 psu at a constant irradiance of $180;{mu}mol/m^2/s$. No growth was observed with a temperature of $15^{circ}C$ and a salinitiy of 15 psu. Moderate growth rates of more than 0.30 /day were obtained at $25^{circ}C$ with salinities of 25.35 psu. These values are similar to in situ observations for this species. The maximum growth rate, 0.35 /day, was obtained at $25^{circ}C$ and 30 psu. In light experiments, cell growth of C. polykrikoides was conducted with constant temperature ($20^{circ}C$) and salinity (30 psu) under light photon flux densities (PFD) of 10, 25, 50, 70, 100, 150, 250 and $350;{mu}mol/m^2/s$. C. polykrikoides did not grow at $10;{mu}mol/m^2/s$. Cell growth was observed at irradiance values of $25;{mu}mol/m^2/s$ and above. The irradiance-growth curve was described as ${mu}=0.30{cdot}(I-15.27)/(I+27.22)$, (r=0.99). This suggests a compensation PFD of $15.27;{mu}mol/m^2/s$ and a maximum growth rate of 0.30 /day. In conclusion, C. polykrikoides prefers high salinity, temperature and irradiance in summer in Korea. These results provide important information for understanding the mechanism of C. polykrikoides blooms and developing technology to predict blooms of this organism in the field.