Intertidal algal communities of Muchangpo and Maryangri in western coast of Korea were investigated qualitatively and quantitatively. Seasonal assessments of species composition, biomass, dominant species in biomass and vertical distributional pattern were conducted from July 1986 to April 1988. Ninety-nine species of marine algae (13 Cyanophyta, 12 Chlorophyta, 24 Phaeophyta and 50 Rhodophyta) were observed, of which 90 (13 Cyanophyta, 11 Chlorophyta, 23 Phaeophyta and 43 Rhodophyta) were from Muchangpo and 83 (10 Cyanophyta, 11 Chlorophyta, 21 Phaeophyta and 41 Rhodophyta) were from Maryangri, respectively. Ordination by detrended correspondence analysis based on the floristic data from nine localities indicated that, on the whole, marine algal distribution in western coast of Korea might be divided into two regions, i.e. the north and the south, being separated at the Taean Peninsula, the mid-western coast. Seasonal fluctuations of mean biomass were 44.55-201.19g-dry wt/$m^2$ at Muchangpo and 19.59-134.76g-dry wt/$m^2$ at Maryangri. Important species determined by the specific proportion of biomass were Sargassum thunbergii, Pelvetia siliquosa and Corallina pilulifera at Muchangpo, and Sargassum thunbergii and Corallina pilulifera at Maryangri.