Purpose Contrast-induced nephropathy (CIN) remains a dreaded complication in the cardiac diagnostic and interventional area. We investigated the relationship between red blood cell distribution width-to-albumin ratio (RAR) and CIN in elderly patients with ST-segment elevation myocardial infarction (STEMI) undergoing emergency percutaneous coronary intervention (PCI). Methods A total of 1532 elderly patients were enrolled and divided into the CIN group and the non-CIN group. The risk factors of CIN were evaluated by univariate and multivariate regression analysis. Receiver-operating characteristic (ROC) curve analysis was used to identify the best predictive value. Results CIN occurred in 129 (8.42%) patients. Patients in the CIN group had significantly higher RAR than those in the non-CIN group (4.69 +/- 0.73 vs. 3.18 +/- 0.64, P < 0.001). In multivariate regression analysis, RAR was an independent risk factor for the development of CIN (OR: 1.506, 95% CI: 1.227-2.083, P = 0.025), along with age, creatinine, eGFR, hs-CRP and contrast agent dose. The AUC of RAR was 0.755 (95% CI 0.703-0.807), and an optimal cutoff value of 3.64 or higher predicted CIN with a sensitivity of 76.2% and specificity of 65.7%. Conclusion As a combined inflammatory-related index, RAR was an independent risk factor for the development of CIN in elderly patients with STEMI undergoing emergency PCI. The RAR could be a simple but relatively reliable parameter for identifying high-risk patients.