The data reported in the update literature on the effects of vitamin C on the nutritional physiology and immunity of fish are compiled and discussed. The vitamin C requirements of fishes usually vary to some degrees by species, size, environmental factors and the chemical or physical status of vitamin C. Three evaluation indices（ growth, tissue concentration and immunity parmneters）are often used to estimate the vitamin C requiement of fish. The vitamin C requirements based on constant tissue concentration of vitamin C are generally higher than those on growth performance. Furthermore, vitamin C requirements based on immunity parameters are much higher than those on contant tissue concentration and growth performance. Usually, high level of dietary vitamin C can increase the resistance to stresses and diseases in fish although there are some study results showing no beneficial effect on the non-specific immunity of fish. The research fields in future are also presented in this review.