A 61-year-old man who complained of right hypochondralgia was diagnosed as hepatocellular carcinoma (HCC) associated with hepatitis B virus (HBV) infection. The tumor was located in the right lobe and S3, and the tumor thrombus extended into the main portal and left portal veins. Preoperatively, real-time tumor-tracking radiation therapy was performed on the tumor thrombus (20 Gy/4 Fr),after vessel coils were placed at the anterior hepatic artery as a marker for the radiation. Ten days after radiation therapy, extended right hepatectomy with thrombectomy and S3 partial hepatectomy were performed. There were no postsurgical complications, and intrahepatic artery infusion chemotherapy was performed. The patient was alive with no recurrences 20 months after surgery. Radiation therapy before hepatectomy is an effective treatment for portal venous tumor thrombus in HCC.