We investigated species composition and variation of benthic marine algae between 2003 and 2006 at Dokdo on the East Sea. The total number of benthic algae species identified was 96, which included 15 Chlorophyta, 30 Phaeophyta, 50 Rhodophyta and 1 Spermatophyta species. The representative species in this study were Ulva pertusa, Caulerpa okamurae, Codium adhaerens, C. frgile, Undaria pinnatifida, Ecklonia cava, Eisenia bicyclis, Dictyopteris undulata, Padina arborescens, Sargassum horneri, Hildenbrandtia rubra, Lithophyllum okamurae, Amphiroa dilatata, Corallina officinalis, C. pilulifera, Prionitis cornea, Grateloupia elliptica, Plocamium telgairiae, Chondrus ocellatus, Chondracanthus intermedia, Chondria crassicaulis, Polysiphonia morrowii, Melobesioidean algae and Phyllospadix sp. Wet weight biomass according to various depths ranged between 1,094.8 to $2,595.3;g;m^{-2}$ during the study period. Mean biomass at the investigated sites was greater in the 15m depth range than in the 5 and 10m depths. Vertical distribution was characterized by Ulva intestinalis, U. linza, Endarachne binghamiae, Bangia atropurpurea, Gloiopeltis furcata and Chondria crassicaulis at intertidal zone, Amphiroa dilatata, Corallina pilulifera, Gelidium amansii, Eisenia bicyclis and Ecklonia cava at 2m depth, Ecklonia cava, Eisenia bicyclis, Padina arborescens, Undaria pinnatifida and Sargasum horneri at 5m depth, Ecklonia cava, Sargassum horneri and Padina arborescens at 10m depth, Ecklonia cava, Myagropsis myagroides, Padina arborescens and Sargassum horneri at 15m depth. The R/P, C/P and (R+C)/P value were 1.67, 0.50 and 2.17, respectively.