Studies on the longevity of the seeds of three rice lines and their F1 hybrids with different moisture contents were conducted. This study found that: the safe moisture contents of male sterile lines and F1hybrids had decreased by 2% as compared with 13% for the maintainer lines and restorer lines, which is the upper limit of national standard moisture content for conventional rice varieties; The seed moisture content of the male sterile line and F1 hybrids is just about 11%, and the variation in longevity tends to show a typical contra-S - shaped survival curve. As the sprouting rate decreased to 80% the survival curve descended rapidly. According to the rules of the typical survival curve, we can set up several new equations to predict seed longvity.