© The Author(s) 2021.We investigated whether the systemic immune inflammation index (SII) on admission is an independent risk factor that predicts the development of contrast-induced nephropathy (CIN) in patients with non-ST segment elevation myocardial infarction (NSTEMI) who underwent percutaneous coronary intervention (PCI). A total of 429 patients with NSTEMI were enrolled in the study. Contrast-induced nephropathy was defined as an increase in serum creatinine level of ≥0.5 mg/dL or ≥25% above baseline within 72 hour after the procedure. Patients were divided into 2 groups: with and without CIN. Demographics, clinical risk factors, angiographic and laboratory parameters, CIN incidence, and SII score were compared between the 2 groups. Non-ST segment elevation myocardial infarction patients, who developed CIN, had higher glucose levels (P =.009), neutrophil counts (P <.001), platelet counts (P <.001), neutrophil-lymphocyte ratios (P <.001), high sensitivity C-reactive protein levels (P =.009), and SII levels (P <.001) than those who did not develop CIN. The receiver operating characteristic curve analysis showed that at a cutoff of 933.2, the value of SII exhibited 77.6% sensitivity and 69.2% specificity for detecting CIN. Our study showed that the SII levels on admission were independently associated with CIN development after PCI in patients with NSTEMI.