Abstract: An 8-week feeding experiment was conducted to evaluate the effects of different monocalcium phosphate (MCP) levels added into high lipid (7.0%) diet on grass carp (Ctenopharyngodon idella) growth performance, lipid metabolism and antioxidant activity. Five levels of MCP (0, 1.0%, 2.0%, 3.0% and 4.0%) were added into high lipid diet, respectively, as basal diets to feed grass carp initial body weight (47.51±0.52) g. Each treatment contained three replicates with 15 fishes per replicate. The results showed that the addition of suitable MCP in high-fat diets could significantly increase the weight gain rate (WGR) and the whole-body phosphorus of grass carp, as well as reduce the Feed conversion ratio (FCR) and Viscerosomatic index (VSI). Taking WGR, FCR and whole-body phosphorus as the observational indicators, the analysis of broken-line model showed that the appropriate amount of dietary MCP was 3.26%, 2.96% and 2.63%, respectively. With the increase of MCP in the diet, the whole-body, viscera, muscle, and liver crude lipid content decreased first and then rose, but the whole-body and muscle crude protein had opposite trends. In the MCP3.0% group, grass carp intestinal amylase, lipase, trypsin, and serum alkaline phosphatase (AKP) had the highest activity, while serum triglyceride, hepatic malondialdehyde and acetyl-CoA carboxylase (ACC) were the lowest. Serum total cholesterol was significantly lower in the supplemented group than in the control group (P<0.05). Liver carnitine acyltransferase (CPT-I) activity increased with the increaseing dietary phosphorus. This study indicates that the optimal supplementation of MCP in grass carp high fat (7%) diets was 2.96%—3.26% (TP 1.43%—1.50%), and the appropriate level of MCP can promote the digestion and utilization of dietary nutrients, as well as reduce hepatic lipid accumulation. At the same time, it also increases protein and antioxidant capacity, and decreases lipid, which help promote growth.