Introduction: The role of urinary neutrophil gelatinase-associated lipocalin (NGAL) as a prognostic biomarker in acute kidney injury (AKI) associated with coronary bypass graft has been suggested in some studies. However, the results have been inconclusive in different studies. Objectives: In the present research, we investigated the diagnostic and prognostic roles of NGAL in Iranian patients who developed AKI after coronary bypass surgery. Patients and Methods: This study was cross-sectional conducted on adult patients undergoing coronary artery bypass graft (CABG) surgery. Postoperative AKI was defined based on the RIFLE (risk, injury, failure, loss and end-stage kidney disease) criteria. Patients were divided into AKI and non-AKI groups. The urinary NGAL and serum creatinine levels were measured at different times after surgery. Results: Out of 29 patients, men constituted 75.9% of cases. Mean age of the patients was 61.4±7.7 years old and the mean duration of surgery was 4.9±0.6 hours. Based on serum creatinine, AKI was diagnosed in 37.9%, 17.25%, and 13.8% of patients at first, second, and third day post-surgery, respectively. The urine NGAL increased by 48.35% and 34.5% at 2 and 6 hours after surgery, respectively. However, there was no significant association between the urinary NGAL level and the incidence of post-surgery AKI. Conclusion: This study showed that urinary NGAL was inapplicable to independently diagnose or predict the outcome of transient AKI associated with CABG.