Background: Cardiac surgery-associated acute kidney injury (CSA-AKI) is a frequent happening affecting nearly 40% of the cases undergoing cardiac surgery. This is associated with increased hospital length of stay and mortality. Objective: The aim of our study was to investigate the relationship impact of modified ultrafiltration on cardiac surgery-associated acute kidney injury (CSA-AKI). Patients and Methods: This prospective observational study was conducted over a 6-month period (February to July 2017) at Cardiothoracic Surgery Unit, Kasr AL-Ainy Hospitals. The study included 40 patients undergoing routine valve replacement surgery using cardiopulmonary bypass. Results: There was no significant difference (P > 0.05) between AKI and non-AKI patients in pre-operative levels while the postoperative serum creatinine levels were significantly higher (P < 0.04) in AKI than non-AKI patients in the modified ultrafiltration (MUF) group. The pre-operative and 2h post-operative S. NGAL was significantly higher in AKI than non-AKI patients in the MUF group were. Duration of CPB was significantly (P < 0.001) prolonged in the AKI than the non-AKI patients. While, there was no significant difference regarding aortic crossclamp time. There was a significant longer ICU stay and duration of mechanical ventilation in AKI than non-AKI patients. Conclusion: Modified ultrafiltration after cardiac surgery is associated with a lower prevalence of morbidity and mortality. Serum Neutrophil Gelatinase-Associated Lipocalin (NGAL) can be used as an early plasma biomarker predictor for AKI in patients undergoing heart surgery