In order to know sea water characteristics around coast line of Cheju Island, physical and chemical environmental factor analyses have been performed with data observed from June 1987 to April 188. Water temperature was over 10℃ even in winter with highest value of 14.7℃ in the southern part over the whole study area. Concentrations of DO, COD and SS were as low as those in the standard sea-water-quality classes [I] and [II]. Nutrient concentration was higher in the present study region than on the coastal areas by previous works, suggesting influx of materials from land. The ratio of N/P ranged from 21.6 to 67.4 (mean : 38.8). Concentration of Chlorophgll-a was high in eastern and southern part throughout the year, except a special high value of 3.89㎎/㎥ at Gosan, western part of the study area, in August.