Background: The nutritional status of the patient is an important parameter in patients undergoing surgery. This study aims to determine of prognostic nutritional index value that predicts hospital mortality and morbidity in on-pump cardiac surgery. Methods: In this study, we scanned the medical data of 1003 patients who underwent on-pump cardiac surgery. Patients’ divided into two groups according to in-hospital mortality. 934 patients without in-hospital mortality were defined as Group I, and 69 patients who died in the hospital were defined as Group II. Their preoperative nutritional status was determined using the prognostic nutritional index classification. Results: In our series, age is statistically higher in Group II rather than Group I (62.5 ± 0.3 vs. 67.4 ± 1.2; p=0.001). There was a significantly different a higher tendency of hospital-acquired infection in Group II (151; 16.2% vs. 44; 63.8%; p=0.001). Postoperative stroke significantly higher in Group II (35; 3.7% vs. 62; 89.9%; p=0.001). Multivariate analysis revealed that cross clamp time, cardiopulmonary bypass time, intraaortic balloon pump usage and intensive care unit stay significantly higher in Group II (p<0.05, respectively). The prognostic nutritional index value was found statistically low in Group II (48.34 ± 6.71 vs. 44.76 ± 7.63; p=0.001). Multivariate analysis revealed that male gender, age, and the prognostic nutritional index were independently associated with postoperative survival. Conclusion: In on-pump cardiac surgery, postoperative mortality and morbidity are significantly associated with preoperative low prognostic nutritional index, and the prognostic nutritional index can be a useful and suitable parameter for preoperative risk evaluation.