Seven hundred rice landraces which were distributed in six geographic groups in China were analysed using nine isozyme loci. The results showed that the genetic diversity of rice was the most in Yunnan, secondly in the Huaihe River. We suggested that there are three centers of genetic diversity for Chinese cultivated rice, i.e. Yunan, the upper reaches of the Huaihe River-the middle and lower reaches of the Yangtze River and South China. The center of origin of Chinese cultivated rice is probably in the middle reaches of the the Yangtze River-the upper reaches of the Huaihe River. Combining with the data of archaeology and other former results, we propose that Yunnan is not the center of origin of Chinese cultivated rice but probably is the secondary center which was strongly influenced by the center of origin of South Asia cultivated rice.