Cholestasis occurs in a variety of clinical settings and often results in liver injury and secondary biliary fibrosis. Several matrix metalloproteinases (MMPs) are upregulated in the liver during cholestasis. The function of the major interstitial collagenase, MMP‐13, in the initial phase of liver fibrosis is unknown. The aim of this study was to evaluate the role of MMP‐13 during the development of cholestasis‐induced liver fibrosis by comparing wild‐type and MMP‐13‐deficient mice. Cholestasis was induced by bile duct ligation (BDL) for 5 days or 3 weeks. Activation and proliferation of hepatic stellate cells (HSCs) were detected by immunohistochemistry. Expression of MMP‐13 mRNA increased significantly in BDL livers of WT mice. After BDL for 3 weeks liver fibrosis was suppressed in MMP‐13‐deficient mice versus WT animals. Activation and proliferation of HSCs were also suppressed in livers of MMP‐13‐deficient mice after BDL. To clarify the mechanism of this suppression, samples from 5‐day BDL mice were used for evaluation of liver injury. Compared with those in WT animals, serum ALT and the number of hepatic neutrophils were reduced in MMP‐13‐deficient mice. Increased expression of the mRNA of inflammatory mediators such as tumor necrosis factor‐alpha (TNF‐α) was significantly suppressed in livers of MMP‐13‐deficient mice. Upregulation of fibrogenic markers, for example, transforming growth factor beta1 (TGF‐β1), was also significantly suppressed in livers of MMP‐13‐deficient mice versus in WT mice. In conclusion, distinct from the known function of interstitial collagenase to reduce liver fibrosis by degrading the extracellular matrix, MMP‐13 contributes to accelerating fibrogenesis in cholestatic livers by mediating the initial inflammation of the liver. (HEPATOLOGY 2006;44:420–429.)