A 26-year-old woman underwent laparoscopic-assisted distal pancreatectomy and splenectomy for a tumor in the tail of the pancreas. Although the preoperative diagnosis was a solid pseudopapillary tumor, pathological tissue examination revealed that the tumor was a pancreatic acinar cell carcinoma. She was treated with S-1 chemotherapy for 6 months without severe side effects, and no recurrence was detected on several imaging inspections. Acinar cell carcinoma of the pancreas is a rare tumor in young patients, and there are few reports of treatment with postoperative chemotherapy.