A 57-year-old man was found to have elevated levels of HCC markers during an observation of chronic hepatitis C. Diffused hepatoma was involved in the posterior lobe, and tumor thrombus extended into the main portal vein (Vp4). Posterior segmentectomy and tumor thrombectomy were performed. But, CT scan 45 days after the operation showed an enhancement at the residual tumor thrombus in the posterior branch. The patient received a hepatic arterial infusion of 5-FU, followed by hepatic arterial embolization. Then, we chose radiation therapy to the tumor thrombus. The most recent CT showed no enhancement at the reduced tumor thrombus. There have been almost no reports of treatment for residual portal thrombus. Careful observations are necessary in such patients.