Abstract: Arsenic (As) is a redox-sensitive element widely distributed in the nature. However, its reliability as a proxy for tracing redox conditions in marine sediments remains controversial. The Sea of Japan, one of the most extensively developed marginal seas of the northwest Pacific, has experienced significant redox condition changes since the Last Glacial Period, making it a natural laboratory for understanding the evolution of sedimentary As. Through high-resolution analysis of As, Mo, and other parameters in sediments from core LV53-18-2, significant variations in As and Mo concentrations over the past 30 000 years in the western Sea of Japan were observed. During the Heinrich Stadial 1 (19～15 ka), the synchronous enrichments of As and Mo indicate anoxic or sulfidic conditions in sediments. In contrast, during the Last Glacial Period (30～19 ka) and the late deglacial – early Holocene (15～8 ka), asynchronous variations between As and Mo occurred. Seasonal sea ice activity not only increased the transport of terrestrial As to the sea but also accelerated the formation of deep water in the Sea of Japan and internal ventilation. Since 8 ka, both As and Mo concentrations were decreased synchronously. The improved global climate and sea level rising conditions enhanced the productivity at sea surface and biogenic material contributions in the Sea of Japan, which diluted the sedimentary As concentrations. Given the complexity of the As enrichment mechanisms in sediments, we suggest that As is not a reliable proxy for tracing redox changes in marine sediments, and its use in paleo-redox reconstructions should be validated in conjunction with other proxies.