As a part of the environmental base line survey of the Onsan Industrial Base, Korea, marine algal communities were investigated using the quadrat method in Onsan-myon on the east coast of Korea from March to December of 1978. It was learned that the representative dominat species along the coast in the Onsan area throughout the year are Ulva pertusa, Pachymeniopsis elliptica, and Sargassum thunbergii. Both the number of algal species occurring in the quadrat (50$ imes$50cm) and the total coverage were higher in March and September than in June and December. A total of 94 species (1 blue-green, 16 green, 25 brown, and 52 red algae) of marine algae was identified in this study.