The in situ observations and the seawater analyses were conducted in July and Auguse, 1996 for the purpose of evaluating the characteristics of seawater quality centered about eutrophication in Mokpo harbour. By applying the OECD standards of trophic classification to the parameters such as secchi depth, total inorganic nitrogen, phosphate phosphorus and chlorophyll-a, the trophic level of seawater in Mokpo harbour was evaluated to be in eutrophic state in summer. The estimation of pollution index by eutrophication showed the seawater quality of Mokpo harbour to deteriorate and fall under the regular grades. The results of eutrophic index estimation showed the high otentiality of red tide occurrence in Mokpo harbour.