A Porites lutea core from Yongshu Reef of Nansha Islands covering 50_year growth history is analyzed for carbon isotopic composition with monthly and seasonal resolution, and the results show that the coral δ 13 C generally has clear yearly cycles. The calibration indicates that the coral δ 13 C can record the sunshine duration, total cloud cast and rainfall of the Yongshu Reef, and it also shows significant association to El Nio events. From 1950 to 1999, the δ 13 C shows a clear long-term declining trend, which indicates a decrease in the sunshine duration and an increase in cloud cast and rainfall over Yongshu Reef over the past fifty years.