Background: Contrast-induced nephropathy (CIN) is an important complication after diagnostic coronary angiography (CAG) and percutaneous coronary intervention (PCI). We investigated the incidence of the development of CIN and the predictive factors for the development of CIN in acute coronary syndrome (ACS) patients undergoing CAG or PCI. Methods: From January 2005 to June 2010, we evaluated the clinical, laboratory and angiographic data of 406 patients with ACS who had serum creatinine value ���1.3 mg/dL and underwent CAG or PCI. The patients were divided into two groups according to the development of CIN (Group I with CIN: n = 92, Group II without CIN: n = 314). Results: Among 406 patients, CIN developed in 92 (22.7 %) patients. Lower baseline body mass index (BMI) (p=0.001), decreased left ventricular ejection fraction (LVEF) (p<0.001), decreased creatinine clearance (CrCl) (p<0.001), lower albumin (p<0.001), lower hemoglobin (p=0.003), higher N-terminal pro B type natriuretic peptide (p=0.001) and larger amount of contrast media volume (CMV) (p=0.021) were associated with group I than group II. By multiple logistic regression analysis, LVEF(<40 %) (OR 0.245; 95% CI 0.125-0.479; p<0.001), CMV(<135 mL) (OR 0.509; 95% CI 0.308-0.841; p=0.008), CrCl(<30 mL/min) (OR 2.096; 95% CI 1.148-3.827; p=0.016), and albumin(<3.5 g/dL) (OR 0.490; 95% CI 0.291-0.825; p=0.007) are independent predictors of CIN. A cut-off value of CMV was 135 mL and that of albumin was 3.55 g/dL. Conclusion: CIN occurred 22.7% in patients with ACS and renal dysfunction, who underwent CAG or PCI. Independent predictors of CIN were decreased LVEF, large amount of CMV, decreased CrCl, and low albumin. Key wards: contrast-induced nephropathy, acute coronary syndrome, serum creatinine