Abstract: In order to study the characteristics of fertility alteration in two new Photo-Thermo Sensitive Genic Male Sterile (P/TGMS) lines, H61S and H69S were observed under controlled conditions and natural conditions by ways of different sowing dates in 2005~2006. The results showed that: (1) Day-length had no obvious influence on fertility transition for the two P/TGMS lines, while temperature was the main factor of fertility transition. (2) The sensitive stages of temperature on fertility expression for H61S and H69S which were 19~10d and 20~10d before heading respectively, were similar to Pei’ai64S (20~19d), and the most sensitive periods were 17~13d for all the three male sterile lines above. (3) The critical temperatures were 24.2℃, 25.3℃, 26.1℃ for H61S, H69S and Pei’ai64S (CK) respectively when the fertile pollen rates was one percent. (4) The two P/TGMS lines had high self-setting rate and long stable sterile period, and so they could be multiplied and produced hybrid-seeds safely, but their fertile periods were short in Zhanjiang. Compared with Pei’ai64S (CK), the periods of fertility alteration for H61S and H69S were shorter.