Abstract: The experiment was conducted to investigate the effects of dietary protein source and stocking density on growth performance, body composition and serum biochemical parameters of grass carp (Ctenopharyngodon idellus). A two-factor orthogonal experiment (3×5) was used to evaluate the effects of soybean meal (SM), Clostridium autoethanogenum protein (CAP), Tenebrio molito (TM), cottonseed protein concentrate (CPC) and Chlorella (CH) for grass carps with three stocking density. Five isonitrogenous and isoenergetic diets were prepared with the five protein sources as a single protein source, respectively. Grass carps with an initial body weight of (5.36±0.18) g were fed with the five test diets at three stocking density (0.11, 0.16 and 0.21 kg/m³_,) for 60 days in pond cages (1.0 m×1.0 m×1.5 m), respectively. The results showed that the feed coefficient (FCR) increased, and the specific growth rate (SGR), weight gain rate (WGR), protein efficiency (PER) and liver index (HSI) decreased with the increase of stocking density. Under the three stocking densities, FCR in TM group was significantly higher than that of other protein source groups (P<0.05), and FBW, SGR, WGR and PER were significantly lower than those in other protein source groups (P<0.05). The growth performance of grass carp in the 0.11 and 0.16 kg/m³ stocking density groups were similar, and were significantly better than that in the 0.21 kg/m³ stocking density group (P<0.05). Protein source and stocking density had no significant effects on the moisture, crude protein and ash content of the whole grass carp (P>0.05). The crude fat content of grass carp in the 0.21 kg/m³ stocking density group was significantly lower than that in other stocking density groups (P<0.05), and the serum biochemical indexes of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and glucose (GLU) were significantly higher than those in other stocking density groups (P<0.05). Regardless of the stocking density, the serum albumin (ALB) content of the CH group was significantly higher than that in the CAP group, the TM group and the CPC group (P<0.05). The alkaline phosphatase activity of TM group was significantly higher than that in the CAP group (P<0.05). Based on the protein efficiency and weight gain rate, the ability of grass carp to utilize the five protein sources was CAP=CH=CPC =SM>TM.