The length of pollen viability after anther dehiscence is crucial to successful pollination (Stone et al1995), particularly for outbreeders. It determines the possibility of outcrossing between species, provided that limited specific reproductive barriers exist. With the rapid development of biotechnology, more transgenic crops, including transgenic rice, are becoming available, resulting in biosafety concerns about possible ecological risks. Evaluation of transgenes introgressing to wild rice species becomes an important issue for rice breeders, environmentalists, and policymakers. Studying pollen viability and longevity of wild and cultivated rice species as well as their hybrids is important in evaluating outcrossing frequencies.