Abstract： Objective To evaluate the therapeutic efficacy and treatment-related toxicity of stereotactic body radiation therapy(SBRT)in patients with medically inoperable stage Ⅰ/Ⅱ non-small cell lung cancer(NSCLC). Methods SBRT was applied to 30 patients, including clinically staged T1 ,T2(≤5cm)or T3(chest wall primary tumors only), N0, M0 ,biopsy-confirmed NSCLC. All patients were precluded from lobotomy because of physical condition or comorbidity. No patients developed tumors of any T-stage in the proximal zone. SBRT was performed with the total dose of 50 Gy to 70 Gy in 10 - 11 fractions during 12 - 15 days. prescription line was set onthe edge of the PTV. Results The follow-up rate was 100%. The number of patients who completed the 1-, and 2-year follow-up were 15, and 10, respectively. All 30 patients completed therapy as planned. The complete response(CR), partial response(PR)and stable disease(SD)rates were 37%, 53% and 3%, respectively. With a median follow-up of 16 months(range,4-36 months), Kaplan-Meier local control at 2 years was 94%. The 2-year overall survival was 84% and the 2-year cancer specific survival was 90%. Seven patients(23%)developed Grade 2 pneumonitis, no grade ＞ 2 acute or late lung toxicity was observed. No one developed chest wall pain. Conclusions It is feasible to deliver 50 Gy to 70 Gy of SBRT in 10 - 11 fractions for medically inoperable patients with stage Ⅰ / Ⅱ NSCLC. It was associated with low incidence of toxicities and provided sustained local tumor control.The preliminary investigation indicated the cancer specific survival probability of SBRT was high. It is necessary to perform similar investigation in a larger number of patients with long-term follow-up.