A 25-year-old Japanese woman with a large abdominal tumor (10 cm in diameter) and high level of serum alpha-fetoprotein (AFP, 1,222.4 ng/mL) was introduced and admitted to our hospital in January 2011. Preoperative imaging modalities could not identify the tumor origin. There was no chronic hepatic viral disease, however, the elevated level of fucosylated AFP (87.8%) and connection with the left hepatic lobe led us to diagnose the tumor as a hepatocellular carcinoma. Surgical resection was performed in February. Histological findings revealed a pancreatic acinar cell carcinoma (ACC). Herein, we provide details of this difficulty to diagnose a case of ACC.