Molluscan shells were sampled from 31 localities in the South Sea shelf (26 in the southeastern continental shelf and 5 in the southwest sea) to understand the sea-level changes and molluscan thanatocoenoses after the last glacial maximum (LGM). At the southeastern continental shelf, 13,074 shell remains were classified into 119 genera and 170 species (Bivalvia: 73 genera and 105 species; Gastropoda: 43 genera and 60 species; Scaphopoda: 3 genera and 5 species). Cluster analyses were used to group the species into 12 assemblages (Glycymeris–Ventricoloidea–Phacosoma [GVPA], Glycymeris–Paphia–Pitar [GPPA], Glycymeris–Cryptopecten [GCA], Glycymeris–Ventricoloidea–Cryptopecten [GVCA], Pecten–Pitar, Ostrea–Limopsis, Dentalium, Nuculana–Cranulilimopsis, Lucinoma–Glycymeris, Pecten–Acila–Siphonalia, Glycymeris, and Buccium), among which the Glycymeris fauna (GVPA, GPPA, GCA, GVCA) occurred at 11 stations, mainly around Tsushima Island on the South Korean shelf. Radiocarbon dates between late Pleistocene and Holocene were determined for 47 dominant and specific species, which were sampled from 24 stations of the South Sea. Fortunately, the habitats of the molluscan species were depth sensitive, allowing for the discrimination of samples into depth-limited age groups. These groups suggested that the sea level fell by about 150–160 m about 15,000 years ago (during LGM), allowing a land bridge to form between the Korean peninsula and Japan. Subsequently the sea rose approximately 60 m about 9000 years ago. Sea level remained at 50–60 m until about 4000–5000 years ago. About 3000–4000 years ago sea level rose to about 10–20 m (below present) and has remained there to the present. Glycymeris fauna were created on the southeastern shelf about 6000 years ago, whereas Arca fauna prospered in the southwestern sea area about 2000–3000 years ago when the sea level was 10–20 m below present.