In order to understand what leads to the appearance of harmful Chattonella algae in the Yeosu coastal waters of Korea, we measured environmental parameters every week at one station from May to November, 2006, and April to October, 2007. Four species of Chattonella appeared during the monitoring period: C. antiqua, C. globosa, C. marina and C. ovata. The range of water temperature and salinity were $15.0-27.9^{circ}C$ and 17.6~33.0 psu, respectively, when Chattonella appeared, and their maximum cell density (4,840 cells/L) was at $27.1^{circ}C$ and 33.0 psu. During the monitoring periods, the range of dissolved inorganic nitrogen (DIN), phosphate (DIP) and chlorophyll $alpha$ (Chl-$alpha$) concentrations in surface waters were $1.20-52.23;{mu}M$ ($8.59{pm}8.97;{mu}M$), $0.03-1.56;{mu}M$ ($0.47{pm}0.31;{mu}M$) and $0.45-31.12;{mu}g/L$ ($3.58{pm}4.77;{mu}g/L$), respectively. Chattonella occurred at low cell density when the Chl-$alpha$ concentration increased because of supplied nutrients, whereas their cell density increased during the periods of rapid decrease in Chl-$alpha$. The results of growth experiments based on batch culture showed that the half saturation constant ($K_s$) of C. antiqua on ammonium (${NH_4}^-$), nitrate (${NO_3}^-$) and phosphate (${PO_4}^{2-}$) were $3.89{mu}M$, $5.01;{mu}M$ and $0.63;{mu}M$, respectively. These Ks values are higher than those reported for diatoms and other flagellates at the DIP concentration (average $0.47{mu}M$) of Yeosu coastal waters. Although the maximum specific growth rate (${mu}_{max}$) of C. antiqua was lower than diatoms, it was higher than those of other flagellates. Therefore, our results indicate that the DIP level in the study area was too low to support Chattonella blooms, although Chattonella species have physiological characteristics that enable them to grow more rapidly than other flagellates when nutrient levels are higher than their $K_s$.