A study on marine sponges was conducted with the materials collected by SCUBA diving in Hongdo and Gageodo Islands, Korea from September 2004 to July 2005. Clathria (Clathria) hongdoensis n. sp. and Clathria (Clathria) sohuksanensis n. sp. turned out to be new to the science. Clathria (Clathria) hongdoensis n. sp. closely seems to C. (C.) acanthstyli Hoshino (1981), based on their spicules type. However, they differ in the size of spicules and growth form. Clathria (Clathria) sohuksanensis n. sp. is similar to C. (C.) bicalthrata Hooper (1996), except for lacking small toxas.