The primary production at 10 stations around the coast line of Cheju Island has been investigated from the viewpoint of standing crops(cells/e), chlorophyll-a concentration and CO₂ fixation of phytoplankton during the period from June, 1987 to March, 1989. Phytoplankton standing crops ranged from 2,025 to133,734 cells/ethrough the year, increasing from June and showing a peak in August. The distribution of standing crops was the highest in the eastern area and the lowest in the northern area. Chlorophyll-a concentration ranged from 0.45 to 2.59 ㎎/㎥ during the study period, which was much lower than that in the other Korean coastal waters. To estimate the CO₂ fixation of phytoplankton, daily primary production (㎎C/㎥/day) has been determined using C-14 method. It ranged 1.31-7.15, 34.54117.04, 22.283.64, 8.53-11.95㎎㎎/㎥/㎥/day in winter, summer, fall, and spring, respectively, and showed the highest in the western area. The carbon assimilation number(㎎C/㎎ chl-a/hr)was also higher in summer than in other seasons. The general characteristics of primary production of phytoplankton around the coast line of Cheju Island was high in the eastern and western regions during the summer season.