The Megavoltage radiotherapy is typically confined to patients with unresectable non-small cell lung cancer and contributes to improve their survival and quality of life. Numerous studies on the prognostic factors of radiation therapy have analyzed histologic types, tumor size, anatomic and physiologic stages and radiation dose. From Jan. 1991 to Dec. 1992, fifty patients with non-small cell lung cancer who were confirmed histologically at Chonnam University Hospital and completed full course of radiation were conducted to analysis for the response rate to radiotherapy according to the histologic types, bronchoscopic finding of endobranchial involvement, anatomic and physiologic stages. The results were as follows: 1. The histologic groups of 50 patients were classified as 40 cases of squamous cell carcinoma, 9 cases adenocarcinoma and 1 cases undifferentiated types. 2. The response rate to radiotherapy including complete and partial remission was 40% in all patients with non-small cell lung cancer and also in only squamous cell carcinoma group. There is no significant difference in response rate between squamous cell carcinoma and adenocarcinoma groups. 3. The response rate to the degree of bronchial obstruction on the bronchoscopic finding tended to be increased in the non-obstructive rather than obstructive group. However, there was no statistically significance. 4. The response rate to types of bronchial obstruction on the bronchoscopic findings was significantly increased in the exophytic than non-exophytic type (p=0.013). 5. The response rate to T stage (tumor extent) by the bronchoscopic determination was significantly better in the T0,1 than other group. 6. The response rates were no significant differences according to the anatomic stagings and performance status scores. 7. The complications following radiotherapy were noted in 82% of patients and included radiation pneumonitis, dry cough, pharyngeal discomfort, and swallowing difficulty etc. These data may conclude that the significant good prognostic factors to radiation therapy was exophytic type in endobronchial lesion of tumor bronchoscopically and subsegmental location in tumor extent.