AbstractWith the fast development of biotechnology, many transgenic crops have been developed and are in the pipelines for environmental release or commercialization. Crop-to-crop transgene flow from transgenic to non-transgenic rice varieties will affect seed purity of non-transgenic rice varieties, which might lead to unwanted biosafety problems. To assess the probability of transgene outflow in rice (Oryza sativa), gene flow experiments were conducted at two confined biosafety experimental sites in Fuzhou of Fujian Province and Sanya of Hainan Province, with the field design of alternating rows of transgenic rice lines and non-transgenic varieties. Three transgenic rice lines containing two insect-resistance genes (Bt/CpTI) and their non-transgenic counterparts (isogenic lines) were used in the experiments to achieve high levels of spontaneous outcrossing. A hygromycin resistance gene tightly linked with the target transgenes was used as a selective marker for identifying transgenic hybrids. Based on examination of 70,056 geminated seeds, we observed low frequencies of transgene outflow (0.275–0.832%) under cultivation of alternating rows between transgenic rice and its non-transgenic counterparts. This result of low crop-to-crop transgene flow in rice at such close spacing can provide scientific support for the safe use of transgenic rice in terms of “contamina-tion” of non-transgenic rice caused by pollen-mediated transgene outflow, if certain isolation measures are taken.