This study aims to investigate the relationship between sea surface temperature variations in southern Taiwan—when the region was still submerged under the ocean and had not yet uplifted during the early Pleistocene—and the Western Pacific Warm Pool. The goal is to understand how El Niño phenomena affected Taiwan under a climate warmer than today.Mudstone samples were collected from the Gutingkeng area in southwestern Taiwan. Two species of planktonic foraminifera were selected: Globigerinoides ruber, which lives in the surface layer, and Neogloboquadrina dutertrei, which inhabits the thermocline. Stable carbon and oxygen isotope analyses, as well as Mg/Ca ratio measurements, were conducted to reconstruct sea surface and thermocline temperatures at that time. 　　The results show that surface water temperature variations in the Gutingkeng area were related to the Western Pacific Warm Pool temperature changes proposed by Wara, M. W. (2005). It can be inferred that between 0.5 and 2.0 Ma, the Kuroshio Current passed through the Gutingkeng Formation area, causing the surface water temperature there to be directly influenced by the Western Pacific Warm Pool. Additionally, Mg/Ca ratio analyses of foraminifera indicate that the temperature difference between the surface layer and the thermocline reached approximately 7°C.