<p>This study evaluated the protective effects of fermented Chinese herbal on manganese (Mn)-induced oxidative stress and pathological damage in the intestines of largemouth bass (Micropterus salmoides). The experiment consisted of two treatments: the Mn exposure treatment and the manganese plus fermented Chinese herbal (Mn + FCHM) treatment. In the Mn exposure treatment, fish were exposed to Mn solutions at concentrations of 0, 0.750, 1.125, and 1.688 mg/L, while being fed a basal diet. In the Mn + FCHM treatment, fish were exposed to the same Mn concentrations but were fed a fermented Chinese herbal diet. Each group had three replicates, with 30 fish per replicate, for a duration of 60 days. The results showed that the growth performance of the largemouth bass in the Mn exposure treatment significantly decreased, with structural damage and oxidative stress observed in the intestines (<i>P</i> &lt; 0.05). In the Mn + FCHM treatment, the WGR, SGR, and CF of largemouth bass significantly increased, while VSI and FCR significantly decreased (<i>P</i> &lt; 0.05); The intestinal villi were relatively intact, the Mn deposition in the intestines decreased, and the intestinal damage was significantly improved; The expression levels of intestinal barrier genes Occludin-1, Claudin, and ZO-1 were significantly increased (<i>P</i> &lt; 0.05); The activities of GSH-PX, T-AOC, CAT, and SOD enzymes were significantly enhanced, and the MDA content significantly decreased (<i>P</i> &lt; 0.05); The gene expression levels of GSH-PX, CAT, and SOD were significantly increased (<i>P</i> &lt; 0.05). This study demonstrates that fermented Chinese herbal is effective in mitigating oxidative stress and pathological injuries in the intestines of largemouth bass (<i>Micropterus salmoides</i>) caused by heavy metal manganese (Mn), thereby promoting intestinal health.</p>