OBJECTIVE To investigate the histological components and solubility of the bile-cast, and to study the pathological course of bile cast formation. METHODS HE staining, bilirubin staining (Gmelin reaction), Masson's staining, alcian blue staining and fibrin staining (weigert's) were performed on the formalin-fixed paraffin-embedded section of the bile cast. Ultrastructure was examined under the scanning electron microscope. Solubility test was also conducted using chymotrypsin, heparin, trypsin solution, HCl and NaOH solution to dissolve the bile-cast. RESULTS The major components of the bile-cast were bilirubin crystals and collagen fibers. Between the mass of collagen fibers there was certain blood vessel structure. Necrosis bile duct structure was not found in the cast. Under the scanning electron microscope, four kinds of crystal morphologies were viewed. There were some mucoid mass and necrosis defluvium epithelial cells in the bile cast. Solubility test showed that the bile cast could be partial dissolved in NaOH solution (pH = 12.5). No dissolution was found in HCl solution (pH = 5.0), chymotrypsin solution, heparin and trypsin solution. CONCLUSIONS Collagen fibers work as framework in the bile cast with bilirubin crystal filling between the framework. The emergence of fibroblast and blood vessels indicated the formation of bile cast might be the course of exudation and organization due to bile duct epithelium damage. Bile cast could be partially dissolved in alkaline solution, but could not be dissolved in acid solution, or in chymotrypsin, heparin and trypsin solutions.