The bivalve molluscan fauna of Ulsan Bay, East Sea coast of Korea, is summarized, based on original and literature data. The fauna consists of 61 species belonging to 20 families. Seven species are identified only to genus level. Two species (Carditellopsis toneana (Yokoyama, 1922), Carditidae and Fulvia hungerfordi (G.B. Sowerby III, 1901), Cardiidae) are new records for the East Sea coast of Korea, and one species (Crenella decussata (Montagu, 1808), Mytilidae) is a new record for Korea. Biogeographically, Ulsan Bay’s bivalve fauna is subtropical with a predominance of tropical-subtropical species, 21 species, or 39% of the total species number, subtropical, 14 species, or 26%, and subtropical-boreal (mostly subtropical-lowboreal), 11 species, 21%, totalling 86%. A remarkable feature of the Ulsan Bay fauna is the presence of tropical-subtropical species not found in Yeongil Bay but common in tidal flats and shallow waters of the Yellow Sea and the southern part of Korea. A cold water mass appearing off the southeast coast of Korea near Ulsan in summer seems responsible for the presence of boreal-arctic species in this area.
