This dataset reports paired annual-resolution Sr/Ca and δ18O measurements of four fossil Porites corals collected from the northern South China Sea. The ages of the fossil corals were determined by U-Th geochemistry, yielding corrected 230Th ages around 4200 years before the present. The Sr/Ca measurements were carried out using an Inductively Coupled Plasma-optical emission spectroscopy (ICP-OES; Agilent 5110) and the δ18O measurements were performed using a stable isotope ratio mass spectrometer (IRMS, GV Isoprime II). The international coral standard JCp-1 was measured along with the samples, yielding an average value of 8.79 ± 0.05 mmol/mol (2SD, n = 8).