Morphotaxonomic accounts are given to three taxa of Sphacelaria, Phaeophyta from Cheju Island; S. tribuloides Meneghinim, S. subfusca Setchell et Gardner, and S. yamdae Segawa. S. tribuloides has tribuliform propagules and produces plurilocular sporangia. S. subfusca has bifurcate or trifurcate propagules, and reproductive structures except propagules are not found. S. yamadae has twice bifurcate propagules and produces unilocular sporangia. Several taxa morphologically related to these three species are menioned. S. tribuloides and S. subfusca are introduced for the first time to Korean flora.