Long-term survival of the patients with biliary tract cancer has been improved due to development of various kinds of therapeutic modalities such as major vessel resection, portal vein embolization, and preoperative biliary drainage to control jaundice and cholangitis. However, patients with advanced stage cancer still have worse overall survival. This indicates that we need to figure out to seek better outcomes for these patients. According to the FUGA trial, a randomized prospective clinical study in Japan comparing Gemcitabine+Cisplatin and Gemcitabine+S-1, the median survival for unresectable biliary tract cancer was 13 to 15 months. And the 3-year survival rate is about 10%. In pancreatic cancer, conversion surgery is becoming more common. A clinical question has arisen as to whether conversion surgery should be performed even in patients with unresectable biliary tract cancer at initial diagnosis if chemotherapy is effective. In the past and in our study, 20-50% of patients with unresectable biliary tract cancer at initial diagnosis can be converted to resectable disease. The long-term survival rate of resectable cases is comparable to the straight forward resection group. Therefore, it is particularly important to note that even if the tumor seems unresectable at the time of initial diagnosis, it may become resectable depending on the effect of treatment. We must make an accurate diagnosis of the extent of the disease and have to perform safe and curative resections.