Antithamnion miharae(Tokida) Itono was investigated in field and laboratory culture. The plant grows in lower littoral zone through out the year in Korea. The gland cells occur scarcely or commonly according to the populations, but the terminal hairs in the female plants are not observed. The structure of vegetative thallus and the reproductive organs in culture are similar to those of field materials, except for the number of gonimoblasts, wich become five to six in contrast to one to three of the field. A typical Polysiphonia-type life history is repeated in culture. This species which produces tetrahedral tetrasporangia is markedly distinguished from Antithamnion glandulifera sensu Kylin (=Antithamnionella glandulifera (Kylin) Wollaston) which produces cruciate tetrasporangia, while the plants reported by Dawson (1962) and Wollaston(1971) as A. glandulifera seem to be conspecific with A. miharae by the fact that they have the tetrahedral tetrasporangia in stead of cruciate ones.