Abstract: Fish health, as well as disease prevention and control, are the key and tricky sectors in aquaculture. It is of great significance to improve fish immunity and disease resistance through nutritional regulation. Iron is an essential nutrient that regulates growth and immunity in fish. The purpose of this study was to investigate the regulatory effects of ferrous sulfate (FeSO₄), methionine chelated iron (Fe-Met), glycine chelated iron (Fe-Gly), and complex amino acid chelated iron (Fe-CAA) as dietary iron source on intestinal health of largemouth bass (Micropterus salmoides). Four isonitrogenous and isolipidic diets with appropriate iron level provided by FeSO₄, Fe-Met, Fe-Gly, or Fe-CAA were designed. Three replicates were set in each group for a 70-day breeding experiment of young largemouth bass. After the experiment, intestinal antioxidant activities of SOD, CAT, and T-AOC were measured in each group. Additionally, the expression of genes and flora related to intestinal health were analyzed and compared. The results showed that the MDA content of FeSO₄ group was significantly higher than that of Fe-Gly and Fe-CAA groups (P<0.05), while the T-AOC activity of FeSO₄ group was significantly lower than that of Fe-Met and Fe-CAA groups (P<0.05). The CAT level of Fe-Met group was significantly higher than that of the other three groups. At the gene level, the expressions of IL-8 and Occludin genes were significantly higher in FeSO₄ group than those in the other groups (P<0.05), while the expressions of ZO-1 and Claudin-1 genes were significantly higher in Fe-Gly and Fe-CAA group than those in FeSO₄ and Fe-Met groups (P<0.05). The expressions of IL-10, IL-6, and IL-15 genes were not significantly affected by iron sources. Further analysis of intestinal flora showed that the bacterial diversity of Fe-CAA group was significantly lower compared with FeSO₄ group (P<0.05). At the phylum level, Firmicutes in Fe-CAA group were significantly down-regulated, while Proteobacteria and Clostriobacteria were significantly up-regulated compared with FeSO₄ group (P<0.05). At the genus level, Plesiomonas, Enterobacter, and Cetobacterium in Fe-CAA group were significantly up-regulated, while Lactococcus and Aeromonas were significantly down-regulated (P<0.05). Correlation analysis of intestinal flora and antioxidant enzymes showed that intestinal MDA activity was strongly correlated with Escherichia-Shigella and Enterobacter. Intestinal T-AOC activity also showed a strong correlation with Plesiomonas and Achromobacter, while SOD activity was strongly negatively correlated with Achromobacter. Additionally, a strong negative correlation was found between intestinal GSH activity and Streptococcus. However, microbial community function prediction analysis showed no significant difference in intestinal microbial community function between the two groups. In conclusion, compared with inorganic iron sources, organic iron sources can improve the intestinal antioxidant capacity of juvenile largemouth bass, reduce the content of MDA, and thus minimize intestinal damage. Meanwhile, the inclusion of iron complex amino acid chelate in the diet is beneficial to maintain the stability of intestinal flora of largemouth bass and improve the abundance of beneficial flora in the intestine.