Abstract: In order to investigate the effect of sodium bicarbonate (NaHCO₃) on intestinal damage in largemouth bass (Micropterus salmoides) under chronic high-temperature stress, juvenile largemouth bass (20.26±0.08) g were fed diets with or without sodium bicarbonate (NaHCO₃, 5 g/kg) for 8 weeks. The results showed that there was no significant difference in the specific growth rate in the NaHCO₃ group compared to the control group at chronic high temperatures. However, the NaHCO₃ group exhibited significantly improved feed efficiency, protein deposition rate, and protein efficiency, along with a marked increase in intestinal amylase and trypsin activities. The addition of NaHCO₃ also significantly enhanced the intestinal total antioxidant capacity (T-AOC), catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. Furthermore, NaHCO₃ up-regulated the expression of cat and gpx1a genes and down-regulated the gene expression of keap1. Meanwhile, the expressions of pro-inflammatory cytokines (il-1β, tnfα, il15) were significantly down-regulated in the group, while the expression of anti-inflammatory cytokine il10 was up-regulated. In addition, the expression of hsp90, hsp70, and hsp60 genes in the intestines of largemouth bass in the NaHCO₃ group was significantly lower than that in the control group. Histologic analysis of the intestinal tract showed that high-temperature stress induced intestinal damage in largemouth bass, and the addition of NaHCO₃ significantly improved the intestinal tissue morphology and up-regulated the expression of intestinal zo1, jam, occludin, and muc2. In conclusion, the addition of 5 g/kg NaHCO₃ to the feed effectively alleviated chronic high-temperature stress-induced intestinal damage in largemouth bass by improving intestinal antioxidant capacity, intestinal inflammation, and intestinal barrier function. These findings may provide a new perspective to improve the intestinal health of fish under high-temperature stress.