Objective To analyze the incidence and risk factors of delirium after cardiac surgery in the elderly patients during hospitalization in intensive care unit (ICU). Methods Retrospective study was performed in a total of 117 patients (over 60 years old) undergoing heart surgery in Nanjing Hospital from March to May 2014. The incidence of delirium was documented during hospitalization. Multivariate logistic regression analysis was used to evaluate the related factors. Results Postoperative delirium occurred in 27 out of the 117 patients, with an incidence of 23.08%. Univariate analysis showed that delirium was associated with left ventricular ejection fraction (LVEF), duration of mechanical ventilation, length of stay in ICU, blood transfusions, hyponatremia, hyperkalemia, and score of Acute Physiology and Chronic Health Evaluation Ⅱ (APACHE Ⅱ) (P＜0.05). Based on multivariate logistic analysis, duration of mechanical ventilation (P＝0.022), low LVEF (P＝0.041) and length of stay in ICU (P＝0.031) were closely associated with postoperative delirium. Conclusion Low LVEF, long time of mechanical ventilation, and long stay in ICU are risk factors for delirium in the elderly after cardiac surgery.