Background: Delirium is one of the most common complications in elderly surgical patients. Although previous studies reported that preoperative malnutrition was related with postoperative delirium (POD), there was lack of evidence to illustrate the relationship between malnutrition and emergency delirium (ED). The objective of this study was to investigate the relationship between preoperative malnutrition and ED in elderly patients undergoing noncardiac surgery.Methods: The study was carried out in accordance with STROBE guidelines. This was a secondary analysis of a prospective cohort study. Elderly patients (65-90 years) who underwent noncardiac surgery under general anesthesia were enrolled in Peking University First Hospital.Preoperative malnutrition was defined as nutritional risk screening 2002 (NRS 2002) ≥3. Emergence delirium was assessed by Confusion Assessment Method for intensive care unit at 10 and 30 min after Post-anesthesia care unit (PACU) admission, and before PACU discharge. Multivariable analysis was employed to analyze the relationship between malnutrition and emergence delirium.Results: 915 patients were enrolled. The incidence of malnutrition was 53.6% (490/915). The incidence of emergency delirium was 41.8% (205/490) in malnutrition group and 31.5% (134/425) in control group, P<0.001. After adjusting confounding factors (i.e., age, mild cognitive impairment, American Society of Anesthesiologists classification (ASA), duration of surgery, pain score, low body temperature and allogeneic blood transfusion), malnutrition was not associated with increased risk of emergency delirium (OR=1.055, 95% CI 0.767-1.452, P=0.742).Conclusions: Malnutrition was common in elderly patients undergoing non-cardiac surgery, but it’s not related with emergence delirium after adjusted for confounders.Trial registration: Chinese Clinical Trial Registry (http://www.chictr.org.cn) (Number: ChiCTR-OOC-17012734).