To assess the efficacy of oral glutamine (Gln) supplementation on clinical and survival outcomes of patients with locally advanced non-small cell lung cancer (LA-NSCLC). Between 2010 and 2014, 122 stage III NSCLC patients were retrospectively analyzed. All patients received curative intent chemoradiotherapy (CRT). Prophylactic oral Gln powder was applied at a dose of 10g tid. Effect of oral Gln supplementation in the prevention of severe (≥grade 2-3) acute radiation-induced esophagitis (ARE) and weight loss, and their relation with overall survival (OS) and disease-free survival (DFS) was measured. Median follow-up was 13.14 months (range; 1.97-55.36). Fifty-six (46%) patients had received oral Gln. Severe ARE was significantly lower in Gln-supplemented group (30% vs 70%; p=0.002). Gln-free patients demonstrated a higher weight loss (p=0.0001). In multivariate analysis hemoglobin (hb) level (<12g/dL; p=0.01) and nodal stage (N3; p=0.01) were poor prognostic factors that affect OS; Weight loss (p=0.06) and Gln-free (p=0.05) reached nearly significant levels that poorly affect OS. Similarly, nodal stage (N3, p=0.014) and Gln-free (p=0.035) were poor prognostic factors that affect DFS. Weight loss (≥2%, p=0.06) and hb level (<12g/dL, p=0.07) reached borderline significance that poorly affect DFS. Nodal stage (N3) was the only poor prognostic factor that affect OS and DFS in univariate analysis (p=0.01, p=0.009; respectively). Oral Gln supplementation significantly reduces grade 2-3 esophagitis and weight loss and also no negative impact on tumor control and survival outcomes in patients with LA-NSCLC.