Starting from the February 2008 till the end of November 2014, abundance of phytoplankton and their composition living in the coastal waters of Kyoungju city were investigated. Environmental and biological properties were also observed at 10 different stations on a seasonal basis. Due to the environmental variables, fluctuating pattern was appeared during the entire period of observation with different degree, as compared to those found in other costal waters in the East Sea. The concentration of phosphate was turned out to be very low which was even less than threshold level in the study area. Phytoplankton community structure was dominated by diatoms (both micro-and nanoplankton fractions) for several years and seasonal succession was also relied on the diatoms. The importance of dinoflagellates in the community was relatively low. Abundance of phytoplankton was heavily affected by physical factors in the surface water, however, affected more by chemical factors including nutrients in the deep water. For periods of this study, the phosphate concentrations was observed in an extremely low, which indicates that the main limiting factor affecting phytoplankton growth could be phosphate.