Abstract: Experiments were conducted to study the fertility change in tbe photoperiod-sensitive genic male sterile rice, Nongken 58 photoperiod-sensitive sterile line (abbr. Nongken 58S). under natural sunshine and different treatments of daylight length. The results revealed that Nongken 58S had two distinct periods of fertility change under natural condition in Guangzhou(23'08N) viz, the first ten days of June from fertility to sterility, the last ten days of August from sterility to fertility. Tbe change of fertility was a process of quantitative alteration to qualitative alteration. Tbe sterility was complete and stable in the sterile period,the fertility ,however, was rather variable in the fertile period. There were only sterile periods and semi- fertile periods in some years. The fertility of Nongken 58S was controlled by environmental factors during the development of the panicle. The panicle at different phase of development showed different sensitivity in the fertility change. Tbe most sensitive was the period from secondary rachis- branch and spikelet primordia to pollen mother cell formation stage. At these stages, the panicles induced by long daylight were completely sterile,but by short daylight, the more tbe days,the higher tbe fertility. The main factors causing fertility change were daylight length,the number of induction days and the temperature. The critical light length for tbe change from fertility to sterility was longer than that for the change from sterility to fertility,and they all shortened with higher temperatures. The number of induction days mainly influenced the development of quantitative alterations into qualitative alterations during the process of fertility change.