Abstract: Plant proteins have been increasingly used as sustainable substitutes for fishmeal in aquafeeds; however, their high inclusion level compromises fish performance. Selenium (Se) is an essential micronutrient required for normal development and antioxidant protection, but its effects on the growth, physiological metabolism, and immunity of marine fish in response to high-plant-protein diets need further research. To investigate the effects of sodium selenite on growth performance, body composition, ppars gene expression, and intestinal inflammatory response of juvenile turbot fed off a high-plant-protein diet. A total of 525 turbot (30.79±0.22) g were randomly divided into 7 groups (3 replicates each): DP, DN, D1, D2, D3, D4 and D5. After a 52-day feeding trial, sodium selenite supplementation alleviated growth inhibition caused by the high-plant-protein diet, improving weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER), and condition factor (CF). Feed coefficient showed the opposite trend and was significantly higher in the DN group than in others. In whole-body composition, crude lipid content in whole fish and dorsal muscle was significantly reduced in the DN group, whereas hepatic crude lipid content was significantly increased. Appropriate sodium selenite relieved hepatic lipid accumulation caused by low fishmeal. Additionally, sodium selenite mitigated the reduction in serum activities (total cholesterol, lysozyme, alkaline phosphatase, and total superoxide dismutase) induced by the high-plant-protein diet. Appropriate sodium selenite inhibited the decrease of pparα1, pparα2, and pparβ mRNA levels and the increase of pparγ mRNA levels induced by the high-plant-protein diet. Sodium selenite also increased TGF-β1 content and decreased TNF-α and IL-6 contents in the intestinal. In conclusion, sodium selenite mitigated the negative effects of the high-plant-protein diets on growth performance, hepatic lipid deposition, immunity, and intestinal health; the recommended supplemental level is 0.6–2.4 mg/kg. This study lays a theoretical foundation for further exploration of sodium selenite in aquatic formulated feeds.