Background: Recently, there have been some reports about the usefulness of expandable metallic stents (EMS) covered with polyurethane membrane (PM) in cases with inoperable biliary malignant strictures (IBMS). These reports provoked us to evaluate histological findings of covered and noncovered EMS in 14 autopsy cases with IBMS. Materials and Methods: For these three years, we have studied 14 autopsy cases with IBMS treated by EMS histopathologically. There are 4 cases of bile duct carcinoma (BDCA), 8 cases of pancreatic carcinoma (PCA), one case of hepatocellular carcinoma (HCC), and one case of gastric carcinoma (GCA) with metastasis to hilar lymph node. Of these 14 cases, 5 were treated by EMS covered with PM. Combined radiation therapy was performed in three out of 8 cases with BDCA. Results: The average days of patency was 191 in the non-covered group (NCG), and 234 in the covered group (CG). Tumor ingrowth was detected in 7 out of 9 (78%) cases of NCG, and in 1 out of 5 (20%) cases of CG. This tumor ingrowth in CG was found in a case of PCA whose patency of EMS was 212 days. Overgrowth was detected in 1 out of 9 (11%) cases of NCG, and 1 out of 5 (20%) cases of CG. The debris in EMS was observed in all (100%) cases of NCG, and in 2 out of 5 (40%) cases of CG. The liver abscess was observed in 6 out of 9 (67%) cases of NCG, and in 1 out of 5 (20%) cases of CG. In the non-cancerous lesion of biliary duct, EMS invaded to the submembranous layer and expanded the muscular layer. Necrosis, fibrosis, and granulomatous changes were found in three cases with BDCA treated by radiation. No case with perforation of biliary duct was experienced. Conclusions. EMS covered with PM may play an important role in preventing from tumor ingrowth, debris and liver abscess in cases with IBMS. PM may contribute to keeping longer patency of EMS in cases with IBMS. The risk of tumor ingrowth should be considered in the case treated by EMS with PM.