Background: Randomized trials have found that treatment with chemotherapy & radiotherapy led to improved survival for inoperable locally advanced non small cell lung cancer patients (NSCLC). Sufficient data is not available in our developing country regarding changes on pulmonary function after radiotherapy in lung cancer. Despite newer technical developments of radiation therapy in treatment of NSCLC, radiation‐induced lung toxicity (RILT) remains a crucial problem. Clinically assessed RILT scores have their limitations, and more objective measures such as pulmonary functions tests (PFTs) might help to improve treatment protocol. Objectives: Assessment of pulmonary function with respect to FEV1, FVC, FEV1/FVC, PEFR, FEF25 – 75%. Material & Methods : All biopsy proven 62 cases of Non small cell carcinoma of lung (NSCLC) were included. All patients received post chemotherapy conventional external radiation 60 Gy in 30 fractions for 6 weeks by Teletherapy Theratron 780e Cobalt60 machines. After clinical assessment, all patients were placed for Pulmonary function tests ( FEV1, FVC, FEV1/FVC, PEFR, FEF25 – 75%) at baseline, 1 month, 3 month after completion of radiation. Spirometric analysis was done by electronic spirometer ( HELIOS 702 ). Data analysis was done by SPSS software. Results: 62 patients were included in this study. All lung function parameter did not shows significant changes after radiation, compared to baseline study. All p value show >0.05. Conclusion: In my study, no statistically significant changes are found in the lung function parameters.