We report a case of an elderly patient, 82 years-old, with initially-unresectable pancreatic head cancer, who successfully underwent complete resection of the primary lesion after systemic chemotherapy for 6 months. The patient had a history of pancreatic body-tail resection for intraductal papillary mucinous carcinoma in 2005. In 2020, a routine examination revealed an increased CA19-9 value of 1,958 U/mL and showed a pancreatic head tumor of 35 mm on CT images. Finally, the tumor was pathologically diagnosed as pancreatic cancer by a biopsied sample. Although CT images showed no distant metastasis, peritoneal lavage cytology was indicated as positivity(H0P0CY1)in the staging laparoscopy. We implanted a peritoneal port and introduced systemic chemotherapy of gemcitabine and nab-paclitaxel combination therapy. This treatment for 6 months induced tumor shrinkage to 30 mm on the CT image, normalized CA19-9 value to 22.6 U/mL, and negative cytology in the collected lavage fluid from the peritoneal port. The patient's general condition was maintained even after the chemotherapy and the lavage cytology was pathologically diagnosed as negative(H0P0CY0)in the repeated staging laparoscopy, therefore we decided to perform pancreaticoduodenectomy as a conversion surgery. The patient was discharged on the 21st postoperative day with an uneventful course and underwent adjuvant chemotherapy of S-1 for 6 months. No recurrence was found in 8 months after the surgery. In such a case of the selected elderly patient with a maintained general condition, it is feasible to undergo multimodal treatments including conversion surgery for an initially-unresectable pancreatic cancer with positive peritoneal cytology.