A 69-year-old woman with a chief complaint of jaundice was referred to our hospital. She underwent exploratory laparotomy under a diagnosis of advanced biliary tract cancer. Histological examination of a biopsy specimen of the gallbladder revealed adenocarcinoma. The tumor was unresectable because of invasion into a wide area of the hepatoduodenal ligament and liver bed. Retrograde transhepatic bile drainage tubes were inserted through the common bile duct into the right and left branches of the intrahepatic bile ducts. After metallic biliary stent implantation, gemcitabine (1,000 mg) was administered intravenously once a week for 2 weeks, followed by 1 week of rest. After 2 courses of chemotherapy, computed tomography showed significant reductions in the size of target tumors and serum CA19-9 levels had normalized. Tumor size was stable for more than 6 months. The patient has been able to maintain a good quality of life without any severe adverse effects of chemotherapy. Gemcitabine therapy after metallic biliary stent implantation might be safe and effective in patients with unresectable gallbladder cancer.