Abstract: The invasion of bullfrog (Rana catesbeiana) has become one of the main factors leading to population decline and extinction of some native amphibians. Although bullfrogs were introduced into mainland China in 1959, they were not wildly raised until 1990. Natural populations of the species in China have never been reported. We investigated bullfrogs in Zhoushan Archipelago and Ningbo area in the east of Zhejiang Province, China. Bullfrogs were found on Xiushan, Liuheng, Daishan and Fodu island. A total of 23 individuals of bullfrogs were captured on these islands from Sep. to Nov. 2003, including 4 adults, 18 juveniles and 1 tadpole. Twenty-eight tadpoles of bullfrogs were captured from Daishan between Jan. and Feb. 2004. This clearly shows that tadpoles of bullfrogs can over-winter and bullfrogs have successfully established their populations in the wild on these islands. Bullfrogs were mainly found in reservoirs, ponds and rivers, and share habitats with 6 indigenous frog species in this area. Escape from farms and release of live bullfrogs abandoned by bullfrog farmers due to falling profits are the main sources of the bullfrog invasion. There will be a great potential threat of bullfrogs to indigenous amphibians in the area. There is an urgent need for greater understanding of the diet, distribution and population dynamics of the bullfrog in China.