Abstract: In order to study the difference in fertility alteration between the main-crop and the ratoon plant of photo- thermo sensitive genic male sterile (P/TGMS) of rice and its correlation to photoperiod and temperature, four P/TGMS lines (Pei’ai64S, GD1S, N9S and Hai3S) were observed under natural conditions in Zhanjiang. The results showed that the ratoon plants of P/TGMS lines had shorter sterile periods but higher fertilities than that of the main-crop, and the degrees of fertility restoration of the ratoon plants among four P/TGMS lines were different. In the same P/TGMS line, however, no difference could be found between ratoon plants caused by trauma or physiological factors. Majority of the coefficients between the pollen fertility of the ratoon plants and the temperature and day length were negatively or significantly negatively related, suggesting that the ratoon plants were more sensitive to temperature and day length compared with its main-crop. The fertility alteration of the ratoon plants could be caused by the increased critical temperature of fertility alteration, and critical temperature of fertility alteration of the ratoon plants were in mean 2.8 ℃ higher than that of the main-crop in four P/TGMS lines.