Cytokeratin 8 (CK8) is a cytoskeletal protein, a member of the keratin family, which plays an important role in regulating epithelial cell adhesion and motility and mediating immune responses. To investigate the role of ck8 in the immune response of largemouth bass (Micropterus salmoides), the full-length sequence of largemouth bass Msck8 gene (2424 bp) was cloned using rapid amplification of cDNA ends (RACE) technology. Among these, the length of 5′ untranslated region (5′ UTR) was 570 bp, the 3′ UTR was 195 bp, and the open reading frame (ORF) was 1659 bp, encoding 552 amino acids, with a predicted molecular weight of 61.30 kD and a theoretical isoelectric point of 5.17. In the phylogenetic tree, MsCK8 proteins were clustered closely with smallmouth bass (Micropterus dolomieu), which showed a high homology. Quantitative PCR analysis showed that Msck8 was expressed in nine tissues of healthy largemouth bass. It was expressed, in descending order, in the heart, muscle, gill, kidney, liver, foregut, hindgut, midgut, and spleen. After immunostimulation with lipopolysaccharide, the expression of Msck8 in muscle, heart, and hindgut of largemouth bass showed prominent temporal changing patterns. The expression levels of Msck8 in the muscle and heart peaked at 6 h. The expression levels in the hindgut showed a positive correlation with temporal sequence and peaked at 48 h. Under high soybean meal stress, the expression level of the Msck8 gene in the experimental group was significantly lower than that in the experimental group (P＜0.05). In conclusion, Msck8 may play an important role in the immune response of fish against bacterial invasion.