The annual variation of algal vegetation at two reefs, A and 3, of Odong-do, Yeosu, was observed two times each month during the period from June 1970 to May 1971, and the results obtained are as follows : 1. The total number of the algal species occurred were 69 species, of which 12 species belong to Chlorophyceae, 17 species to Phaeophyceae and 40 species to Rhodophyceae. No significant difference was noticed in the occurrence number of algal species at the reefs observed. 2. Most species of the algal communities in each algal belt did not show seasonal variations, but the following species showed fluctuations iii cover degree : Ulva pertusa, Enteromorpha sp., Sphacelaria sp., Scytosiphon iomentaria, Colpomenia sinuosa, Sargassum thunber gii, Pterocladia tenuis, Amphiroa ephedrea, Carpopeltis affinis, Gigartina tenera, Polysiphonia yendoi, Chondria crassicaulis, Symphyocladia atiuscula. 3. The species occurred in each algal belt at all two reefs did not show much variations and the main species in each belt are as follows: $200\~150cm$ belt - Gloiopeltis complanata, G. furcata, Enteromorpha sp., etc. : $150\~100cm$ belt - Ulva pertusa, Chondria crassicaulis, Sargassum thunbergii, etc. ; $100\~50cm$ belt - Gigartina tenera, Pterocladia tenuis, Scytosiphcn lomentaria, Polysiphonia yendoi, etc ; Below 50cm- Sargassum sagamianum, Cystophyllum sisymbrioides, Gelidium amansii, Acresorium yendoi, Microcladia elegance, etc. 4. The species occurred below 100cm level were almost the same at A and B reefs, but those above 100cm level at the A leef were different from the B reef; th: species of the algal belt of reef A were composed of Gloiopeltis complanata, Corallina pilulifera, Chondria crassicaulis, Sargassum thunbergii, Polysiphonia yendoi, Ulva Pertusa, etc., and those of reef B were composed of Gloiopeltis complanata, G. furcata, Enteromurpha sp. and Ulva pertusa, thus the main composition of reef B was very simple. 5. According to Taniguti's classification of marin: algal com nunity, the reefs observed belong to the Gigartina intermedia-Sargassum sagaminnum association (Sargasseto-Gigartinetum Taniguti) of Myelophycus caespitosus alliance (Myelophycion Taniguti).