The patient was a 76-year-old man who was admitted to our hospital with a diagnosis of ileus. A gallbladder tumor was found incidentally on CT, and it was diagnosed as gallbladder cancer. Enlargement of multiple lymph nodes, including the paraaortic lymph nodes, was observed, and PET-CT further showed FDG uptake in the lymph nodes. Based on these findings, the patient was diagnosed with Stage ⅣB gallbladder cancer with paraaortic lymph node metastases. Since surgical resection was not possible, chemotherapy with gemcitabine and cisplatin(GEM plus CDDP)was started. After completion of 4 courses of GEM plus CDDP, the enlarged lymph nodes were decreased in size on CT, and there was no FDG uptake on PET-CT. These findings indicated downstaging to Stage Ⅱ; thus, conversion surgery with extended cholecystectomy and lymph node dissection was performed. The pathological diagnosis confirmed that the patient had Stage Ⅱ cancer(pT2N0M0). A case of unresectable gallbladder cancer that was treated with GEM plus CDDP and subsequent conversion surgery is reported, along with a literature review.