A taxonomic study on marine sponges was conducted by SCUBA diving at Gageodo Island, Korea from August 1999 to July 2001. Among them, Haliclona (Gellius) coreana n. sp. turned out to be new to science. This new species seems to be close to H. (G.) arcoferus Vosmaer, 1885, based on the type of spicules. However, it is different in size of toxa and growth form. Toxa of the new species is half in length compared to H. (G.) arcoferus. The growth form is jar shaped in this new species, but flat in H. (G.) arcoferus.