This study aims to evaluate the impact and potential prognostic roles of the pre- and post-treatment Glasgow prognostic score (GPS) and the change thereof in patients with advanced head and neck cancer undergoing concurrent chemoradiotherapy (CCRT). We collected GPS and clinicopathological data of 139 stage III, IVA, and IVB head and neck cancer patients who underwent CCRT between 2008 and 2011. Their GPSs pre- and post-CCRT and the change thereof were analyzed for correlations with recurrence and survival. The GPS changed in 72 (51.8%) patients, with worse scores observed post-CCRT in 65 (90.3%) of the GPS changed patients. Patients in the improved GPS group showed a tendency toward better survival. From the multivariate analysis, the post-CCRT GPS level was an independent prognostic factor in addition to tumor stage. After CCRT, a high GPS was revealed to be an important predictor of survival for advanced head and neck cancer.