Procambarus clarkii, we evaluated the effects of dietary lysine levels on growth performance, feed utilization, body composition,digestive enzyme activity of this species. Seven isonitrogenous (28.26% crude protein) and isocaloric (17.15 gross energy) diets were formulated with protein sources from the mixture of casein, gelatin, wheat and crystalline amino acid (AA) mixture. The measured lysine levels of the experimental diets were 0.76%, 1.00%, 1.22%, 1.47%, 1.69%, 1.89% and 2.18%. Each diet was fed to four groups of 12 crayfish with an initial body weight of (7.60±0.01) g in floating net cages (60 cm×60 cm×60 cm). The crayfish were fed three times daily for 60 d. The results indicated that weight gain rate (WGR), specific growth rate (SGR), and feed efficiency ratios (FER) all increased significantly with increasing dietary lysine levels (<0.05), and their maximum values were attained at 1.69%, 1.69%, and 1.22%, respectively. However, they all decreased with further increasing dietary lysine levels. Survival rate ranged from 89.58% to 97.92%, and showed no significant difference among all the dietary treatments (>0.05). Whole-body moisture content of crayfish fed 1.22% dietary lysine was significantly lower than that of crayfish fed 0.76% dietary lysine (<0.05), but showed little difference from that of the other treatments (>0.05). The highest whole-body protein and lipid content was observed in crayfish fed 1.89% and 1.69 dietary lysine, respectively. They were both significantly higher than that of crayfish fed 0.76% lysine (<0.05), but showed little difference with that of the other treatments (>0.05). No significant dierence was found in whole-body ash content, muscle composition, muscle AA contents, or digestive enzyme activity among all the treatments (>0.05). The second-order regression analysis of WGR against dietary lysine levels indicated that the optimal dietary lysine requirement of red swamp crayfish) was 1.66% of diet (5.87% of dietary protein).