Background/Aims: Gallstone pathogenesis is linked to mucin hypersecretion and bacterial infection. Several mucin genes have been identified in gallbladder epithelial cells (GBECs). We investigated MUC expression in cholesterolassociated gallbladder disease and evaluated the relationship between mucin and bacterial infection. Methods: The present study involved 20 patients with cholesterol stones with cholecystitis, five with cholesterol stones with cholesterolosis, six with cholesterol polyps, two with gallbladder cancer, and six controls. Canine GBECs treated with lipopolysaccharide were also studied. MUC3, MUC5AC, MUC5B, and MUC6 antibodies were used for dot/slot immunoblotting and immunohistochemical studies of the gallbladder epithelial tissues, canine GBECs, and bile. Reverse-transcription polymerase chain reaction was performed to evaluate MUC3 and MUC5B expression. Results: MUC3, MUC5AC, MUC5B, and MUC6 were expressed in the normal gallbladder epithelium, and of those, MUC3 and MUC5B exhibited the highest expression levels. Greatly increased levels of MUC3 and MUC5B expression were observed in the cholesterol stone group, and slightly increased levels were observed in the cholesterol polyp group; MUC3 and MUC5B mRNA was also upregulated in those groups. Canine GBECs treated with lipopolysaccharide also showed upregulation of MUC3 and MUC5B. Conclusions: The mucin genes with the highest expression levels in gallbladder tissue in cholesterol-associated diseases were MUC3 and MUC5B. Cholesterol stones and gallbladder infections were associated with increased MUC3 and MUC5B expression.