Background: Malnutrition is prevalent in esophageal cancer patients which affects cancer prognosis. The purpose of this study was a comprehensive assessment of nutritional status during Chemoradiation (CRT). Methods: Newly diagnosed adults with esophageal cancer were recruited for this study. Patient-Generated-Subjective Global Assessment (PG-SGA), anthropometric indices, body composition, dietary intake, laboratory tests, and nutritional-related complications were assessed before, after, and 4 to 6 weeks after CRT. Results: Seventy-one cases were enrolled. The mean age was 66.8±12 years. Patients' mean weight loss was 2.42±2.4 kilograms during treatment. A significant reduction observed in mean MUAC (26.68±4.9 vs. 25.42±5.1 cm), fat mass percentage (24.11±11.8 vs. 22.8±12.5), fat free mass index (16.87±2.4 vs. 16.47±2.6 kg/m 2 ) and hand grip strength (43.2±19 vs. 36.1±20 kg) during CRT (all p-values <0.0001). We had also a non-significant change in mean energy intake (19.5±11 vs. 18.3±11 kcal/kgw. day) and protein intake (0.56±0.4 vs. 0.66±0.5 g/kgw.day) during CRT. In our assessment before, immediately after and 4-6 weeks following CRT, we recorded energy intake insufficiency in 55.7%, 58.7% and 27.3% and protein intake inadequacy in 89.8%, 89.1% and 72.7% of cases, respectively. The most common complications were dysphagia (56.7%), anorexia (25%), and constipation (47.9%) at admission. Dysphagia improved in some cases (42%), but anorexia (35%), early satiety (25%), Esophagitis (25%), dysosmia (21%) and dysgeusia (17%) were increased as CRT complication. yet, 25% of patients had dysphagia and 34.4% had constipation 4-6 weeks after CRT. The twelve-months mortality was significantly associated with lower BMI after CRT, primary PG-SGA score, weight loss, BMI<18.5, MUAC, physical performance, living in rural or urban areas, addiction. Conclusion: Our study demonstrated a high prevalence of malnutrition among esophageal cancer patients which worsened during Chemoradiotherapy. Our findings warrant early screening and monitoring of nutritional status and effective nutritional interventions with symptoms management during treatment in these patients.