Abstract: This trial aimed to investigate the effects of astaxanthin (AST) on serum diamine oxidase activity, D-lactic acid content, intestinal antioxidant capacity, intestinal morphology, and the expression of histamine H1 receptor and pro-inflammatory factor genes in juvenile American eels (Anguilla rostrata) under dietary histamine stress. A total of 400 fish with an initial weight of (25.01±0.17) g were divided into four groups: the control group fed a basal diet, the H group fed a diet with a high level of histamine (662 mg/kg), the H+Ast 4 group fed the high histamine diet with 4 mg/kg AST, and the H+Ast 8 group fed the high histamine diet with 8 mg/kg AST. Each group had four replicates with 25 fish per replicate, and the trial lasted for 10 weeks. The results showed that supplementation with the 4 and 8 mg/kg AST in the high histamine diet significantly decreased diamine oxidase activity and D-lactic acid content in the serum (P<0.05), improved intestinal glutathione peroxidase, superoxide dismutase, and catalase activity (P<0.05), reduced malondialdehyde levels (P<0.05), enhanced intestinal villus length and muscular thickness (P<0.05), and reduced the expression of histamine H1 receptor and pro-inflammatory factor genes (P<0.05). However, compared to the H+Ast 4 group, an 8 mg/kg AST diet did not provide further improvements in these parameters. In conclusion, this study demonstrates that the addition of 4 mg/kg AST can alleviate intestinal health problems of juvenile A. rostrata induced by dietary histamine stress. These results provide valuable insights into the use of AST to mitigate dietary histamine stress and its scientific application in the eel feed.