L- ascorbyl- 2- monophosphate (AMP) was used as a vitamin C source to investigate its effects on growth performance and nonspecific immunity of red swamp cray-fish (Procambarus clarkii). Six experimental diets (AMP0, AMP15, AMP30, AMP45, AMP60 and AMP75) with different levels of AMP (.00, 141.01, 280.44, 419.06, 558.13 and 692.09 mg kg−1 diet, respectively) were fed to juvenile crayfish (aver-age weight: .70 ± .01 g) for 56 days. At the end of the 56- day trial, the highest final body weight, specific growth rate (SGR), phenoloxidase activity, lysozyme activity, superoxide dismutase activity and anti- superoxide anion activity all occurred in the AMP30 group (p < .05). Compared with the AMP0 group, crayfish fed with AMP- supplemented diets showed significantly higher hepatosomatic index value (p < .05). Conversely, the feed conversion ratio value of crayfish fed with AMP- supplemented diets was significantly reduced relative to that of the AMP0 group (p < .05). AMP15 to AMP30 diets showed significantly higher muscle rate value, crude protein content, total haemocyte count and blood cell respiratory burst activity (p < .05). Broken- line regression analysis on SGR indicated that the optimal dietary AMP level of red swamp crayfish was estimated to be 300.95 mg kg−1 diet