Morphological and anatomical characters of Amphiroa misakiensis Yendo are investigated with field materials and taxonomic accounts are given to the species. The plants grow on rocks, mussels or non-articulated corallines from the subtidal zone of Cheju island, and is characterized by recumbent and spreading habit from the substrate. The species is well defined by about 4 cm height, loosely tufted thallus with irregularly dichotomous branches, flat and irregularly broad intergeniculum in upper part, geniculum developing by cracking and sloughing of calcified cortical tissue overlying uncalcified genicular tissue, five to thirteen-tiered geniculum with unequal length, and conceptacles buried in cortices of intergeniculum. Reproductive structures in tetrasporangial, male and female plants are typical of Amphiroa. The structure and developmental patterns of conceptacles are very similar to those shown in previous studies.