In order to understand the status of distribution and population density of Crab-eating Frog (Fejervarya cancrivora),we made field surveys at 12 sites of mangrove in Hainan from April to August 2008,and measured the population density and habitat by line transects at the four mangroves.The Crab-eating Frog only found in 4 nature reserves,named Hainan Dongzhai Harbor Mangrove National Nature Reserve,Qinglan Harbor Mangrove Provincial Nature Reserve,Wenchang,Xinying Harbor Mangrove,Danzhou,and Wucun Mangrove Nature Reserve,Chengmai.All the four mangroves have larger area (>100 hm²),rich plant species and exposed bottom at high tide.The average population densities of Crab-eating Frog in mangrove,shrimp pond and intertidal mudflat are 132±71 individuals/hm²,65±50 individuals/hm²and 37±22 individuals/hm² respectively,and the population densities are significantly different among the three habitats.In the four mangroves,the highest population density occurs at Hainan Dongzhai Harbor Mangrove National Nature Reserve and lowest at Wucun Mangrove Nature Reserve respectively.The population density is not different between Qinglan Harbor Mangrove Provincial Nature Reserve and Xinying Harbor Mangrove (P>0.05).The population decline and distribution region reduction of Crab-eating Frog are mainly caused by habitat destruction,water pollution and illegal harvest.