The threatened status of large and middle mammals on Zhoushan Islands has been studied according tocomparison of historical records and analysis of fur purchase data in this paper. The results show that therehave been 16 species of mammals on the islands, 5 species of which have been extinction, and 3 species ofwhich are endangered, and the distribution area of 3 species of which have been decreased (the population ofone of 3 species is being reduced), the population of 2 species of which is stable, and the population of 2species has no data. The extinction percentage of carnivores is larger than that of herbivores. The extinctionpercentage of large mammals is higher. The extinction percentage of species on islands is higher than on thenear by land. The methods determining population trend have been discussed.