The genic male-sterile rice (GMSR) sensitive to photoperiod during the panicle development period is a novel type of germplasm in rice, which is sterile under the long-day condition but fertile under the short-day condition. The fertility is also affected by temperature. A number of GMSR lines have been popularly used in commercial seed production of hybrid rice in China. Because the sterility is decided by environmental factors, a set of fertility conversion indices has been proposed to evaluate the usability and to determine the suitable regions for safe application of these male sterile lines. In the present experiment, 13 photoperiod-sensitive (PGMSR) lines that are dominant in China were sown by stages in the field at Hainan Island (18° 14′ N), Quiyang (26° 35′ N) and Wuhan (30° 38′ N) in China. The fertility and sterility were distinguished on the percentage of seed-setting on the bagged panicles (PBS). The fertility conversion indices were determined on the day-length and temperature regimes and on a fertility quantifying model, and comparison was made between the two methods. Results showed that it was feasible to determine the fertility conversion index of GMSR lines based on data of bagged seed-setting rates in experiments of sowing at different times in the field. Of the 13 sterile lines observed, two of the PGMSR were found to be completely sterile when the length of the day exceeded 12·3 h. Five temperature-sensitive (TGMSR) lines had fertility conversion indices of 24 °C. One of the photoperiod- and temperature-sensitive (PTGMSR) lines showed that steady fertility conversion occurred under the short day in spite of high or low temperature. These GMSR lines are adaptable to the conditions of day-length and temperature in the main rice-growing regions of China and thus of high value in application to seed production.