The incidence of acinar cell carcinoma among malignant pancreatic tumors is about 1%, and the prognosis is reported to be poor. We resected an acinar cell carcinoma that had arisen on the pancreatic head by pancreaticoduodenectomy in December 1983. This tumor occupied the pancreatic head, and it measured 10 X 9.5 X 9.5 cm. The microscopic findings showed that the tumor cell was well-differentiated and acinar formation was uniform. The growth of the tumor was expansive, and the lesion was clearly capsulated by fibrous tissue. There was no lymph node metastasis, so the curative operation was performed by the enbloc resection of the tumor. Zymogen granules in the tumor cells were confirmed by electron microscopy. Consequently, we concluded that the origin of the tumor was acinar cells.