The standard chemotherapy for the treatment of unresectable advanced and recurrent biliary tract cancers is considered gemcitabine plus cisplatin (GC) on the basis of favorable results reported in the ABC-02 study from the UK and the BT22 study from Japan. However, the GC cohort of the BT22 study consisted of only 42 patients, and we considered it necessary to confirm the effectiveness and safety of GC chemotherapy in a multicenter prospective observational study in Fukuoka. Thirty-seven patients were enrolled in this study, including two patients with recurrent disease. The median patient age was 67.5 years (range, 43-84 years). Twelve patients had intrahepatic cholangiocarcinoma, 13 patients had extrahepatic cholangiocarcinoma, and 12 patients had gallbladder cancer. The median survival time (MST) was 14.9 months, the 1-year survival rate was 54.5%, and the median progression free survival (PFS) was 7.7 months. No chemotherapy-related deaths occurred, and Grade 3/4 adverse events were mainly hematological events including leucopenia in 13 (35.1%) patients and neutropenia in 12 (32.4%). The MST, 1-year survival rate, median PFS, and rate of Grade 3/4 adverse events in our study were similar to those of the BT22 study. In conclusion, this multicenter prospective observational study confirms the effectiveness and safety of GC chemotherapy for the treatment of unresectable advanced and recurrent biliary tract cancers.