The species composition and phylogeographical features of marine algal flora of Dok island are investigated. A total of 253 species, 26 green, 67 brown, 160 red, were counted cumulatively since first report by Kang and Park (1969) from Dok island. Among them Ectocarpus corticulatus Saunder, Antithamnion okiense Kajimura are first reported from Korea and Feldmannia irregularis, F. globifera, Spatoglossum crassum newly added by this study. And also, a candidated new species, Dictyota sp. (Dictyotaceae, Phaeophyceae) is collected in this study. A remarkable increasing of warm water brown algal species, eg. Nemacystus decipiens, Sphaerotrichia divaricata, Tinocladia crassa, Petrospongium rugosum, Sargassum yezoense, are observed recently studies. This phenomenon is presumed to be closely related with global warming. For phylogeographical study of marine algae of Dok island we selected two species, one red alga Griffithsia japonica Okamura and one brown alga Dictyota coriacae (Holmes) Hwang, Kim et Lee, which have low dispersal capacity by their Oogamious sexual reproduction. The Dok island's haplotype of G. japonica is clearly distinguished from Oki island haplotype but closely related to the Korean type's haplotypes which distributed in south and east coast of Korea. And also, the Dok island's haplotype of D. coreacea is a unique Korean type which discriminated from Japanese and Taiwanese type. From these results, we proposed the marine algae of Dok island, at least in case of warm water species, were originated from Korean coasts rather than western coast of Japan by the Korean warm current.