Patients with acute coronary syndromes (ACSs) undergoing percutaneous coronary intervention (PCI) are at high risk of contrast-induced acute kidney injury (CI-AKI), a complication associated with poor clinical outcomes. Serum albumin (SA) levels are associated with cardiovascular mortality. We assessed the association between SA levels and the risk of CI-AKI in patients with ACS (n = 890) treated with PCI. Patients were divided into 2 groups: patients with and without CI-AKI. Contrast-induced acute kidney injury was defined as an increase in serum creatinine (≥25% or ≥0.5 mg/dL) from baseline occurring 72 hours after PCI. The SA levels were significantly lower in patients with CI-AKI than in those without CI-AKI (3.52 ± 0.40 vs 3.94 ± 0.39 mg/dL, P < .001). On multivariate analysis, SA was an independent predictor of CI-AKI (odds ratio 0.177, 95% confidence interval 0.080-0.392, P < .001) together with age, female gender, creatine kinase-myocardial band, and glomerular filtration rate. Baseline SA levels are inversely associated with CI-AKI after PCI for ACS.