Abstract: To clarify the effects of vitamin C supplement in diet from different sources on the growth performance and tissue vitamin C content of Cyprinus carpio, four levels of coated-ascorbic acid (CAA) or ascorbic acid polyphosphate (LAPP) (50, 100, 150, and 200 mg/kg, vitamin C effective content in diet) were used. The experiment period was 60 d. The results showed that the optimal vitamin C effective content of LAPP and CAA requirements were 100～200 mg/kg diet and 150～200 mg/kg diet in koi juveniles, respectively. The fish groups of 150 mg (LAPP)/kg diet and 200 mg (CAA)/kg diet had the maximal vitamin C content in muscle and liver. And the liver vitamin C concentrations were higher than that of the muscle vitamin C concentrations. In conclusion, LAPP had advantage over CAA in promoting the growth of Cyprinus carpio.