The study of marine terraces, which include a paleo-shoreline record, provides information on global sea level fluctuations and crustal uplift rates during the Late Quaternary period. This data is helpful in preparing for sea level rise in the upcoming 'Global boiling'. Currently, widely recognized sea level fluctuation curves are derived from oxygen isotope stages in ice cores and deep-sea cores. The data shows a 30-50m sea level fall during Marine Isotope Stage (MIS) 5d-5a. However, some studies conducted in various parts of the world have reported smaller declines in sea level than is commonly known. For instance, studies on the marine terraces of the east coast of the Korean Peninsula suggest that sea level may have been as low as -5 to -10 m during MIS5a and MIS5c. In this study, we investigated the marine deposits in Haenam, located on the southwestern coast of the Korean Peninsula. We found deposits in the sedimentary layers that correspond to MIS5c, which were located beneath layers formed during MIS5e. The age of the sediments was determined using optically stimulated luminescence (OSL) dating. Based on the altitude, formation process, and absolute age of the sediments, it is inferred that sea level was similar to the present during MIS5c in Haenam. Recent research on the southwestern coast of the Korean Peninsula has accumulated data on marine deposits formed during MIS5a and MIS5c. This paper presents the results of studies on sea level during MIS5a and MIS5c on the west and south coasts of the Korean Peninsula. This study suggests one perspective for MIS5a and MIS5c sea level across East Asia and to raise new questions. Specifically, the paper questions why sea levels are similar to present during what is known to be a glacial period. This study offers a fresh perspective on sea level fluctuations in East Asia and can improve our comprehension of the intricate correlation between sea level and climate change.