Abstract: Objective To explore the prevalence of nutritional risk, undernutrition and application of nutritional support in cancer patients during chemoradiotherapy. Methods A total of 80 were enrolled from March 2010 to February 2011 .Nutritional risk screening(NRS 2002) was performed on first 48 hours incharge and the discharged day, Nutritional support was evaluated on the discharged day too. Results Overall prevalence of nutritional risk and undernutrition on first 48 hours incharge was 38.75% , 23.75% respectively, the prevalence of nutritional risk and undernutrition on the discharged day was 81.25%,40% respectively. Totally 20 patients with NRS≥3 were received nutritional support. Grade 3 or higher myelosuppression occurrence were 29%(9/31), 26.5%(13/49) among patients with NRS≥3 and NRS <3 respectively . Grade 4 anemia and thrombocytopenia only occurred in patients with NRS≥3. Conclusions A large proportion of cancer patients is at nutritional risk or undernutrition during chemoradiotherapy .The application of nutrition support is inappropriate. Assessing the nutrition risk dynamically, and carrying out effective nutrition support are the key points to prevent chemoradiotherapy patients from undernutrition.