AIM: To explore the mechanism of benign biliary stricture.METHODS: A model of trauma of bile duct was established in 28 dogs. The anastomosed tissues were resected and examined by light and electron microscopes on day 3, in wk 1, 3 and mo 3, 6 after operation. CD68, TGF-β1 and α-SMA were examined by immunohistochemical staining, respectively.RESULTS: The mucosal epithelium of the bile duct was slowly recovered, chronic inflammation lasted for a long time,fibroblasts proliferated actively, extracellular matrix was over-deposited. Myofibroblasts functioned actively and lasted through the whole process. The expression of macrophages in lamina propria under mucosa, TGF-β1 in granulation tissue,fibroblasts and endothelial cells of blood vessels, α-SMA in myofiroblasts were rather strong from the 1st wk to the 6th mo after operation.CONCLUSION: The type of healing occurring in bile duct belongs to overhealing. Myofibroblasts are the main cause for scar contracture and stricture of bile duct. High expressions of CD68, TGF-β1 and α-SMA are closely related to the active proliferation of fibroblasts, extracellular matrix overdeposition and scar contracture of bile duct.