We measured stable oxygen isotope compositions and trace-element ratios (Mg/Ca, Mn/Ca, and Al/Ca) of the planktonic foraminifera Trilobatus sacculifer from IODP Site 368-U1501 in the northern South China Sea. A total of 324 sediment samples were collected at ~20 cm intervals between 142.42 and 203.25 m CSF-A. The stable isotope dataset spans approximately 19.8-12.2 Ma, whereas the Mg/Ca, Mn/Ca, Al/Ca, and Mg/Ca-derived sea-surface temperature records cover approximately 18.2–13.9 Ma. The chronology is based on an age model constrained by biostratigraphic datums, magnetic polarity reversals, published ⁸⁷Sr/⁸⁶Sr ages, and alignment of planktonic foraminiferal δ¹⁸O to the global benthic δ¹⁸O stack. Stable isotope analyses were performed on well-preserved T. sacculifer tests using a Finnigan MAT 253 mass spectrometer coupled to a Kiel V carbonate device at the State Key Laboratory of Marine Geology, Tongji University. Trace-element ratios were measured on cleaned T. sacculifer tests using a Thermo VG-X7 ICP-MS at Tongji University. Sea-surface temperature estimates were calculated from measured T. sacculifer Mg/Ca ratios using the global multispecies sediment-trap calibration of Anand et al. (2003), Mg/Ca = 0.38 exp(0.09T), after correcting for secular changes in seawater Mg/Ca following Evans and Müller (2012), with the seawater Mg/Ca reconstruction of Stanley and Hardie (1998). Residual seawater δ¹⁸O after correction for the global ice-volume signal (Rohling et al., 2021), here referred to as δ¹⁸Osw-ice, was used to infer relative changes in surface seawater δ¹⁸O and freshwater balance in the northern South China Sea. These data were used to reconstruct sea-surface temperature and surface-ocean hydrographic variability in the northern South China Sea across the Miocene Climatic Optimum and its termination.