The Oki Islands are divided into two districts, namely Dozen and Dogo, Lying between latitudes 35゜59゜N. and 36゜21'N. and between longitudes 132゜56'E. and 133゜24'E.. The Islands are washed by Tsushima Warm Current all along the coasts, and their open coasts are often exposed to violent waves during typhoon and monsoon seasons from early autumn to late winter. The Oki Islands has been reported to have 15 species of Cyanophyceae, 37 species and two varieties of Chlorophyceae, 77 species of Phaeophyceae, 125 species, one variety and two forms of Rhodophyceae two species of sea grass as the marine flora. The list in this report consists of 17 species of Cyanophyceae, 33 species and one variety of Chlorophyceae, 74 species of Phaeophyceae, 102 species, one variety and two forms of Rhodophyceae including the following 14 species which were collected by myself this time and are new records for the Oki Islands. Sphaeronema lithophila and Hypoglossum barbatum are also new records for the Japan Sea, and Kallymenia crassiuscula and K. sessilis have this vicinity as northern boundary of their distribution in the Japan Sea furthermore. Sphaeronema lithophila, Phormidium crosbyanum, Oscillatoria nigro-viridis, Ulothrix flacca, U. implexa, Monostroma nitidum, Schimmelmannia plumosa, Kallymenia crassiuscula, K. sessilis, Antithamnion nipponicum, Ceramium paniculatum, Hypoglossum barbatum, Zostera nana, Halophila ovalis.