We herein report the first case of metastatic pancreatic leiomyosarcoma derived from the urinary bladder diagnosed by an endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) in a 65-year-old woman. The patient had undergone total cystectomy for bladder leiomyosarcoma. Four years thereafter, a nodule was observed in her left lung on chest computed tomography. Suspecting primary lung cancer, pulmonologists at our hospital recommended a thoracoscopic lung biopsy, which the patient refused. Five years post-cystectomy, fluorodeoxyglucose positron emission tomography revealed enlargement of the left lung nodule and a new mass in the pancreatic head. She was referred to our department for the pathological diagnosis of a pancreatic head mass by an EUS-FNB. The EUS-FNB yielded adequate pancreatic tissue for an immunohistochemical analysis. A diagnosis of metastatic pancreatic lesion originating from the urinary bladder was made. In atypical pancreatic tumors, the utilization of an EUS-FNB and immunohistochemical analysis can help establish an accurate diagnosis.