Six species of the genus Symphyocladia are currently recognized worldwide, all of which are reported to grow on the Korean coast. We described a new species Symphyocladia glabra sp. nov. based on morphological and molecular evidence. The new species is characterized by mostly an erect and broad thallus, the parallel arrangement of numerous apical cells, completely fused congenital cells, a corticated basal portion of faint midrib with six to eight pericentral cells, rhizoids cutting off from pericentral cells, and absent vegetative trichoblasts. The new species has morphological similarity to S. marchantioides and S. jejuinsula. However, S. glabra sp. nov. is distinguished from S. marchantioides by the corticated lower portion of the thallus and the absence of vegetative trichoblasts, and S. jejuinsula by number of pericentral cells and the fact that the thallus does not taper upward. The phylogeny of rbcL sequences indicated that S. glabra sp. nov. is definitely a separate entity within the genus Symphyocladia.