The biogeography and diversity patterns of the marine bivalve molluscan fauna of the East Sea coast of South Korea are analyzed. The total species richness of the continental Korean bivalve fauna, excluding insular regions (Dok-do and Ullung-do), is 304, and from north to south the species richness of bivalves increases showing a clear gradient: Gangwon, 143 species ${ ightarrow}$ Gyeongbuk, 131 ${ ightarrow}$ Gyeongnam, 183. A zonal-geographical analysis of the entire fauna shows that the great majority are warm-water mollusks, constituting 77% (subtropical, 37%, tropical-subtropical, 30%, subtropical-boreal, 10%), The number of boreal (low-boreal, widely distributed boreal and circumboreal) species is lower, 19%, whereas boreal-arctic mollusks have only 4%. This demonstrates that the bivalve molluscan fauna of the eastern coast of Korea is subtropical, and has more affinities to the fauna of the East China Sea than to the northern East Sea. Separate analysis by provinces shows the increasing role of warm-water mollusks from north to south. While tropical-subtropical and subtropical species constitute 47% (68 species) in Gangwon, their dominance increases to 71% (93 species) in Gyeongbuk, and to 80% (148 species) in Gyeongnam. The Gyeongnam bivalve fauna is the most diverse in species composition and has the largest number of "endemics" (species known only from this province), 46%. The Gangwon fauna also contains many "endemics", up to 40%, while Gyeongbuk is an intermediate zone with low "endemicity", only at one-fifth of the regional fauna, and has the most species in common among the three provinces.