Abstract: 【Objective】To investigate the effects of adding berberine(BBR) and poly-β-hydroxybutyrate(PHB) to feed on the growth, immunity and intestinal flora of largemouth bass(Micropterus salmoides) in the inverse-season fry.So as to provide theoretical basis for the application of BBR and PHB in the feed for largemouth bass and the inverseseason fry breeding of largemouth bass. 【Method】Largemouth bass inverse-season fry(body mass 130.34±0.26 mg) were used as test materials, and fed basic feed as control(CK), feed B(1‰ BBR), feed P(1‰ PHB), feed BP(1‰ BBR+1‰ PHB) in B, P and MIX groups respectively, and BP5, BP7 and BP14 groups were fed with feed B and feed P alternately at the frequency of every 5, 7 and 14 d. The largemouth bass was cultured for 30 d. The growth performance, liver and intestinal biochemical indexes were measured, and the intestinal flora structure and function were analyzed. 【Result】In growth performance, compared with CK, the final total mass was significantly higher(P<0.05, the same below), and the feed coefficient was significantly decreased in all treatment groups except P and MIX groups; the weight gain rate and survival rate in the BP5, BP7 and BP14 groups were significantly higher than that in CK; the final total mass, survival rate and weight gain rate were the highest in BP7 group while the feed coefficient was the lowest. In the liver, ACP and AKP activities were significantly higher in the B, P, BP5, BP7, BP14 and MIX groups than in CK, while GOT and GPT activities were significantly lower than CK. In the intestine, compared with CK, the contents of MDA and IL-6 were significantly lower in other treatment groups, while the contents of CAT and LZM were significantly increased; the content of TNF in BP5 and BP7 groups was significantly lower than that in CK. At the phylum level, the relative abundance of Proteobacteria was decreased and that of Firmicutes was increased in the BP5, BP7 and MIX groups, relative abundance of Bacteroidota in the BP7 group increased obviously compared with CK. At the genus level, compared with CK, the relative abundance of Achromobacter decreased greatly and that of Lactobacillus increased greatly in the BP5 and BP7groups. Microbial functional genes were significantly enriched in metabolic pathway and environmental information processing pathway in BP7 group. 【Conclusion】Adding BBR to the feed can improve the growth performance of largemouth bass in autumn, and the addition or mixing of BBR and PHB can effectively improve the immunity and antioxidant ability of the fish, improve the liver damage, and reduce the intestinal inflammatory response, and the best effect is achieved by alternating the feeding of BBR-containing feeds with PHB-containing feeds at a frequency of every 7 d. It is assumed that BBR and PHB change the structure and function of largemouth bass intestinal flora and improve liver and intestinal health