The cross-compatibility between cultivated rice and 6 diploid and tetraploid wild rice species was studied st W gm th at by means of artificial pollination. The germination and growth of different wild rice pollen grains on the a of the same cultivated rice were observed with optical-microscope, and the cross results were compared those of cultivated rice at the correspon Oryza rufipogon pollen grains were similar to g time. The results showed that the germination and growth of those of cultivated rice. The pollen grains germinated quickly, after cross. For instance, few numbers of pollen grains adhered to the stigmata; the time when germination started after cross was delayed; few numbers of pollen grains germinated; some pollen tubes failed to enter the stigmata, they just twined or circled on the surfaces of the stigmata after germination; Some pollen tubes could enter the stigmata and grew slowly. No germination was observed in the tetraploid wild rice. According to the results, the relationship between O. rufipogon and cultivated rice is relatively close, and they had good crosscompatibility. On the other hand, O. officinalis and cultivated rice had bad cross-compatibility. It could be concluded that potential gene flow between transgenic rice and O. rufipogon was very large, and was very low between transgenic rice and O. officinalis or other wild rice species.