The aims of this study were to investigate the impact of weight loss experienced during initial Concurrent Chemoradiotherapy (C-CRT) on survival outcome of patients with stage III Non-Small Cell Lung Cancer (NSCLC). We retrospectively reviewed 98 patients with stage III NSCLC who received CCRT from January 2007 to December 2010. Patients were treated with systemic chemotherapy regimen of Cisplatin/Docetaxel and concurrent thoracic radiotherapy at a median dose of 66 Gy (range 60 to 70 Gy). Weight loss was defined as weight loss of more than 5% during C-CRT. In 60% of the patients weight loss was observed. In our retrospective clinical study, Kaplan-Meier curves show that patients with weight loss have poorer Progression-Free Survival (PFS) and Overall Survival (OS) (P=0.005, 0.001). Multivariate Cox regression analysis indicated that weight loss could influence the overall survival time of patients in stage III NSCLC, with the hazard ratio of 1.869 (95% CI, 1.175-2.975; P=0.008). Weight loss may be a useful prognostic factor to predict treatment outcome in stage III NSCLC treated with C-CRT.