We present a calibrated, high-resolution 18O/16O and 13C/12 record for a well-preserved Last Interglacial Porites sp. coral (U-Th age of 127 ± 6 ka) from the sea-level high-stand terrace of Yonaguni Island, Japan. Seasonal variations in the δ18O and δ13C values for the fossil coral are greater than those observed in modern coral records from the same reef setting and appear to be driven by the enhanced insolation seasonality in the northern hemisphere during the Last Interglacial maximum. The 18O enrichment of 1.1‰ in the fossil coral compared to the modern analogue cannot be due entirely to a reduction in sea-surface temperature because corals in this region are already growing at their lower thermal limit. Instead, most of the 18O enrichment must be due to a change in the δ18O of the surface seawater, probably in response to enhanced evaporation of the ocean or a higher volume flux of the Kuroshio Current.