A 7-week feeding experiment was conducted to evaluate the effects of dietary sodium butyrate on protein metabolism and its related gene expression of triploid crucian carp (Carassius auratus tripl). A total of 450 triploid crucian carp with an average body weight of (6.02±0.16) g were randomly assigned to 5 groups with 3 replicates per group and 30 fish per replicate. Five isonitrogen and isocaloric experimental diets were formulated by adding 0 (control), 1.0, 2.5, 5.0 and 7.5 g/kg sodium butyrate (30% microcapsule coated sodium butyrate) to the basal diet, respectively. The fish in the 5 groups were randomly fed one of five experimental diets. The results showed that the supplementation of 1.0 to 7.5 g/kg sodium butyrate significantly improved the contents of serum total protein (TP), albumin (ALB), and globulin(GLB) (P<0.05), and it also improved the serum ALB/GLB, aspartate aminotransferase (AST) activity and glucose (GLU) content, but only the serum ALB/GLB in 2.5 and 5.0 g/kg sodium butyrate groups, serum AST activity in 2.5 g/kg sodium butyrate group, and serum GLU content in 5.0 g/kg sodium butyrate group reached a significance level compared with the control group (P<0.05). Compared with the control group, the contents of serum non-essential free amino acid were sometimes increased and sometimes decreased, and the change was not evident. Only the content of serum lysine was decreased continuelly, the serum other essential free amino acid contents were essentially firstly increased and then increased with the sodium butyrate supplemental level increasing, and had the highest values when the sodium butyrate supplemental level was 2.5 g/kg. Compared with the control group, the intestinal aminopeptidase N (APN) gene relative expression level in 1.0 and 2.5 g/kg sodium butyrate groups was significantly decreased (P<0.05), while the intestinal glutamate dehydrogenase (GDH) gene relative expression level in 2.5, 5.0 and 7.5 g/kg sodium butyrate groups was significantly increased (P<0.05). The results indicate that optimal supplemental level of sodium butyrate can increase the protein metabolism level and its related gene expression of triploid crucian carp, and the recommended supplemental level of sodium butyrate is 2.5 g/kg which is based on the growth indices and production costs.