The surface ultrastructure and epithallium shedding were observed on the following seven species of articulated coralline algae from Hakodate: Amphiroa zonata, Alatocladia modesta, Bossiella cretacea, Calliarthron yessoense, Corallina officinalis, C. pilulifera and Corallina X. The morphology and arrangement of epithallial cells were different between the two subfamilies Amphiroideae (A. zonata) and Corallinoideae (the remaining species), but epithallium shedding occurred in all species examined, removing fouling microalgae and bacteria. When the zoospores of Laminaria japonica were cultured on living and dead C. yessoense as well as microscope slides, germlings didn't grow on the living plant, but florished on the other substrata. The surface observation under scanning electron microscope revealed that the peeling off of epithallium works as cleaning effect for C. yessoense. From these results, it was concluded that the shedding of epithallium in articulated corallines plays a role on antifouling.