Background: Acute coronary syndrome (ACS) refers to a spectrum of clinical presentations ranging from those for ST-segment elevation myocardial infarction (STEMI) to presentations found in non–ST-segment elevation myocardial infarction (NSTEMI) or in unstable angina. Contrast-induced nephropathy (CIN) is defined as the impairment of renal function-measured as either a 25% increase in serum creatinine (SCr) from baseline or a 0.5 mg/dL (44 µmol/L) increase in absolute SCr value—within 48-72 hours after intravenous contrast administration. Objective: To evaluate blood urea nitrogen to left ventricular ejection ratio and TIMI risk index as predictors for occurrence of CIN in patients with acute coronary syndrome who underwent PCI. Patients and Methods: it included 300 patients (68% male and 32% female), mean of age is 57.4 ± 11.5 years old, with a range from 27 to 80 years old and 68% of them are male at Cardiology Department, Faculty of Medicine, Zagazig University; and Cardiology Department, National Heart Institute starting from July 2019 till July 2020. Results: Patients were classified into two groups: CIN group vs non CIN group and we found that, hypotension positive inotrope, history of HF and history of TIA or stroke, were statistically high significant predictors for CIN, showed a statistical significant positive correlation between BUN\EFr level and BUN, creatinin level before and after PCI, TIMI risk index, contrast volume and mehran score and showed that sensitivity of BUN\EFr level as a predictor of CIN was 88.9% with ability to exclude 94.5% of truly negative cases, while sensitivity of mehran score in prediction of positive cases was 100% and 90% exclusion of negative cases, both tools had high accuracy above 90% and a high statistically significant tool used in prediction of CIN. Conclusion: CIN is a frequent complication following PCI and is associated with complicated hospital stay and high mortality rate. Patients who are older and have associated comorbidities such as anemia, acute heart failure, high contrast volume and ratio, high TIMI risk index, high Killip score, high Mehran score and renal insufficiency at the baseline are at High risk of developing CIN. Those patients can be identified, and more vigilant preventive measures can then be applied for the prophylaxis of CIN. BUN/EFr and TIMI risk index score can be used to predict acute kidney injury in patients with ACS undergoing PCI