Tunicates were collected from three harbors (Gampo, Bangeojin, Daebyeon) in Gyeongsangnam-do and one harbor (Seogwipo) in Jejudo Island during the period from August 2008 to January 2011 and were identified on the basis of their morphological characteristics. Among them, colonial tunicate Clavelina lepadiformis (Muller, 1776) belonging to the family Clavelinidae was found to be an invasive alien species introduced from the North Atlantic, and this is the first record of its occurrence in Korea.