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Data on the late Quaternary tephra layers, tephrostratigraphy, geochemistry and environment were determined in two sediment cores from the southwestern part of Ulleung Basin (East Sea/Sea of Japan), representing marine-oxygen isotope stages 1–3. The cores consist mainly of muddy sediments that are partly interbedded with silty sands, lapilli tephra and ash layers. The lapilli tephra layers (Ulleung-Oki tephra, 9.3 ka) originating from Ulleung Island consist mainly of massive-type glass shards, whereas the ash layers (Aira-Tanzawa ash, 22.0–24.7 ka) derived from southern Kyushu Island are mainly composed of typical plane-type and bubble-wall glasses that are higher in SiO2 and lower in Na2O + K2O than the lapilli tephra layers. Except for the tephra layers, fine-grained sediments throughout the core sections are mostly of marine origin based on geochemical data (C/N ratios, hydrogen index, S2 peak) and Tmax. In particular, organic carbon contents increased during Termination I, probably as a result of an influx of the deglacial Tsushima Current through the Korea Strait. [ABSTRACT FROM AUTHOR]