In the management of hepatocellular carcinoma (HCC), a tumor thrombus occurrence between the hepatic vein and right ventricle is life threatening. We studied the effectiveness of radiation therapy to the venous thrombosis between the inferior vena cava and right ventricle. CASE 1: A 66-year-old man who suffered from no hepatic viral infection had hepatectomy of the huge HCC (over 20 cm) and recurrence at the post dperated liver and lung. After transarterial embolization, he suffered from dispnea and was found with tumor thrombus from the left hepatic vein to right atrium. Radiation therapy to the tumor thrombus was done and dispnea disappeared. He died by pneumonia at 5 months after the radiation. CASE 2: A 74-year-old woman who had hepatecomy and RFA for multiple HCC. For the recurrence of HCC, TAE and RFA were performed. After the tumor thrombus in the inferior vena cava, mammarian cancer was found and radiation therapy was performed. She died after 4 months from lung edema, but no growth of tumor thrombus was found. CASE 3: A 79-year-old man who had TAE, hepatectomy, RFA and MCT for multiple hepatoma. After these treatments, tumor thrombus at the right ventricle was found. Although he suffered from portal tumor thrombosis, lung metastases, bone metastases and colon cancer after the radiation therapy, he is still alive at the 19 month of treatments. Radiation therapy is safe and effective for venous tumor thrombosis of HCC.