Abstract: The aim of this study was to investigate the effects of high dietary N-carbamylglutamate (NCG) contents on serum biochemical indicators, liver fat deposition, body fat content, and fat metabolism genes expression in tilapia (Oreochromis niloticus). Tilapia of 360 with an average body mass of (36.56±1.12) g were divided into 3 groups, each with 3 replicates containing 40 fish per replicate. The control group received basic feed without the addition of NCG, while two experimental groups received feed supplemented with high concentrations of 2000 and 5000 mg/kg NCG, respectively. The tilapia were fed twice daily at a rate of 4% body weight. After 8 weeks, the addition of high dietary NCG contents increased the hepatosomatic index of tilapia, with the hepatosomatic index of the NCG II group significantly increased (P<0.05). Liver histological analysis using HE-staining and oil red O-staining showed vacuolar degeneration and significant lipid droplet accumulation in liver cells of the high concentration NCG addition group. Moreover, the tilapia liver in the NCG II group exhibited larger vacuoles and more concentrated lipid droplets compared to the NCGI group. High concentration NCG addition significantly increased the visceral fat content of tilapia while significantly reducing visceral protein content (P<0.05). Serum triglycerides and cholesterol levels in the NCG I and NCG II groups were significantly higher than those in control group (P<0.05). Furthermore, the activities of alanine aminotransferase and aspartate aminotransferase in tilapia serum were significantly increased in the NCG II group (P<0.05). Consumption of high concentrations of NCG led to a significant decrease in the expression levels of genes related to lipid oxidation and decomposition in tilapia liver (P<0.05), including carnitine palmitoyltransferase 1 (cpt1), peroxisome proliferator activated receptor a (ppara), and uncoupling protein 1 (ucp1). In summary, the addition of high dietary NCG contents caused abnormal fat metabolism in tilapia, leading to elevated serum triglycerides and inducing severe symptoms of fatty liver. This effect may be attributed to the decrease in gene expression related to liver fatty acid β-oxidation caused by high dietary NCG contents.