Ｏｂｊｅｃｔｉｖｅ　To evaluate the association between preoperative estimated glomerular filtration rate and the risk of postoperative delirium in elderly patients.　Methods　The current study was a secondary analysis based on data from a randomized controlled study where 700 elderly patients were admitted to the intensive care unit (ICU) after noncardiac surgery. The preoperative estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration equation. Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) was used to evaluate the occurrence of delirium twice a day in the first 7 d after surgery. Univariate Logistic regression analyses were performed to identify potential factors associated with the development of postoperative delirium, and factors with P<0.05 were included in a multivariate Logistic regression model to analyze the risk adjusted association between preoperative eGFR and postoperative delirium.　Results　The median of preoperative eGFR of all enrolled 700 patients was 72.0 ml·min-1·1.73m-2. The incidence of postoperative delirium was higher in patients with low preoperative eGFR (<72.0 ml·min-1·1.73m-2) than those with high preoperative eGFR (≥72.0 ml·min-1·1.73m-2) (19.1% vs. 12.6%, P=0.017). After correction for confounding factors, higher preoperative eGFR was associated with a lower risk of postoperative delirium (OR=0.990, 95%CI 0.980-1.000, P=0.041), a preoperative eGFR <72.0 ml·min-1·1.73 m-2 was an independent risk factor of postoperative delirium (OR=1.796, 95%CI 1.157-2.789, P=0.009).　Conclusions　For elderly patients admitted to ICU after noncardiac surgery, a low preoperative eGFR is associated with an increased risk of postoperative delirium.