The reported incidence of radiation pneumonitis (RP) has varied widely in clinical studies ranging from 0% to 54%. This wide range is probably the result of differences in its precipitating factors. This study aimed to find out the predictive factors of RP in patients with NSCLC who were treated with concurrent chemotherapy and radiotherapy (CCRT). We prospectively studied 76 lung cancer patients who were treated with CCRT consecutively between January 2011 and May 2013 in the Department of Radiation Oncology at Cancer Institute, Assiut University. Radiographic images, pulmonary function tests and symptom assessment were used for the diagnosis of RP. Of the studied 76 patients, 25 patients developed RP (33%), 15 of them developed grade 2 RP, 8 patients developed grade 3 RP, 1 patient developed grade 4 toxicity, and 1 patient developed grade 5 toxicity. In multivariate analysis, FEV1 value (p = 0.000) and chronic obstructive pulmonary disease (COPD) (p = 0.012) were the most significant factors associated with RP. Pretreatment FEV1 value and COPD are useful indicators for predicting RP in NSCLC patients treated with CCRT. Pretreatment of pulmonary function and base-line pulmonary disease is critical for patients’ well being after chemoradiotherapy.