Adenosquamous carcinoma of the pancreas (ASCP) is very rare, comprising only 1–4 % of exocrine malignancies of the pancreas. Several reports have described surgical outcomes for ASCP, but there are few reports of radiotherapy. We treated a case of ASCP with radiotherapy with 50.4 Gy in 28 fractions. The tumor disappeared completely at the end of the radiotherapy but recurred rapidly within the radiation fields, and multiple liver metastases with ascites developed 2 months after treatment, which indicated the possibly high radiosensitivity of the tumor. Initial serum levels of carcinoembryonic antigen, 8.6 ng/mL, and squamous cell-related antigen, 45.8 ng/mL, decreased to within normal limits at the end of radiation therapy, but these 2 tumor markers increased rapidly thereafter.