Abstract: Objective To evaluate the therapeutic efficacy and radiation complications of late course three-dimensional conformal radiotherapy (3DCRT) in patients with stage Ⅲ non-small cell lung cancer (NSCLC). Methods Eighty-six patients with stage Ⅲ NSCLC were randomly divided into group A (n=42) receiving conventional radiotherapy at the total dose of 66 to 70 Gy in 33 to 35 fractions completed in 6 to 7 weeks and group B (n=44) with late course 3DCRT at the dose of 24-30 Gy in 6 fractions (400-500 cGy per fraction every other day) after 40 Gy conventional radiotherapy, completed in 5 to 6 weeks. Results The efficacy rates in groups A and B were 55.0% and 82.9%, and the complete remission rates were 7.5% and 31.7% respectively, showing significant difference between the two groups (P<0.05). The 1-and 2-year survival rates of the patients in group A and B were 62.5% vs 78.0%, and 40.0% vs 53.7% respectively, without significant difference (P>0.05). The median survival time in groups A and B were 11.4 months and 19.8 months respectively. The major radiation complications observed in the two groups were gradeⅠtoⅡacute radiation esophagitis and hematopoietic toxicity. The later stage radiation complications in the two groups were gradeⅠtoⅡradiation lung fibrosis, occurring at a similar rate between the two groups. Conclusion Late course 3DCRT produces better therapeutic effects than conventional radiotherapy in patients with stage Ⅲ NSCLC.