Abstract: Objective:To evaluate the clinical outcomes of patients after intensity modulated radiation therapy (IMRT) for hepatocellu -lar carcinoma (HCC) with portal vein tumor thrombosis (PVTT) or inferior vena cava tumor thrombosis (IVTT). Methods:A registry data -base of41patients treated with IMRT for HCC with PVTT or IVTT in Radiotherapy Center of No.3 Hospital of Beijing Chinese People Armed Police Forces between January 2013and May 2015were analyzed retrospectively. The biological effective dose of radiation was ranged 48- 94Gy. Short-term effects and prospective efficacy were observed. Log-rank test, Cox regression were used for survival analysis and prognostic factor identification. Results: Grade 2 or higher level gastrointestinal reaction was observed in 12patients (29. 3% ). Hematological toxicity was observed in 11patients ( 26. 8% ), and radiation- induced liver disease was observed in6 patients (14. 6%). We found that29. 3% of patients achieved a complete response and 31. 7% of patients achieved a partial response. The stable and progressive disease rates were 39. 0% and 0. 0%, respectively. Median patient survival was11months, and the 1-year survival rate was 34. 1%. The significant independent variables associated with the overall survival included Child Pugh grade, AFP test, and CHE lev -el. Conclusion: IMRT is a safe and effective treatment for PVTT or IVTT in patients with HCC.