Introduction: Delirium is a syndrome characterized by impaired consciousness and changes in cognition. Which lots of patients after coronary by-pass graft have several neurological complications, This study aimed to recognize some risk factors related to delirium in patient who had a by- pass operation.Materials and Methods: this cross-sectional study was conducted on 370 patients ranging from 18 to 85 years old and hospitalized in intensive care unit after coronary artery bypass graft surgery. Risk factors assessed including demographic variables, Diabetes Mellitus, drug abuse and smoking, hypertension, history of stroke and previous surgery, hematocrit lower than 30 percent, psychological disease. The convenience sampling method was used. After ending surgery and the separation from mechanical ventilation, the patients’ mental status was daily examined by means of observational Delirium Screening Scale until they were discharged and transferred from ICU to the surgical ward.Results: The incidence of delirium is reported 23%. There is a significant relation between the incidence of delirium and variables such as atrial fibrillation, psychological disease, Income level and range of hematocrit. Discussion and Conclusion: According to the results, screening and diagnosis of delirium after cardiac surgery is very important. With attention to individual profile and postoperative factors related to delirium, it is necessary to train about economic condition, product of blood and corrects this, underlying disease in order to decrease of delirium.