The extremely high temporal resolution (nearly daily interval) measurement was conducted on the coral (Porites lutea) oxygen isotope compositions (δ18Oc) to examine the detailed relationship between δ18Oc and sea surface temperature (SST) and seawater oxygen isotope composition (δ18Ow) from Hainan Island, China. Although SST and sea surface salinity (SSS) or δ18Ow varied in a wide range at the studied site, the dynamic range of δ18Oc recorded in coral was much smaller than expected from SST and SSS (δ18Ow) changes. The extremely high (>30¿C) and low (<22¿C) SST and low (<27) SSS are not suitable for coral calcification, and coral could not record the information as their skeletal δ18O. Estimated coral extension rates (the overall rate is 15 mm/year) varied by a factor of about 18 within one year, from very slow in winter to very fast in spring. Light availability could affect the extension rate of coral skeleton through the activity of photosynthesis of symbiont algae. Such cessation and acceleration of calcification cause a serious distortion of the δ18O profile, which makes it difficult to make a correlation between δ18O and SST. Because high and low extension rates correspond to low- and high-density bands, respectively, a detailed examination of the density structure may assist the correction for distortion of the δ18O profile.