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. Pre-operative 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.