Abstract: Objective To investigate the impact of lymphocyte-to-C-reactive protein ratio (LCR) on contrast-induced acute kidney injury (CI-AKI) in patients with ST-segment elevation myocardial infarction (STEMI) after emergency percutaneous coronary intervention (PCI). Methods Patients who were diagnosed with STEMI and underwent successful PCI treatment at Suining County People's Hospital between February 2022 and August 2024 were included and their clinical data were collected for retrospective analysis. Logistic regression was used to identify risk factors for CI-AKI. Restricted cubic splines (RCS) were used to determine the dose-response relationship between LCR and CI-AKI. The predictive performance of different models was evaluated using receiver operating characteristic (ROC) curves, net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Results A total of 671 patients were included in the study, with an incidence of CI-AKI during hospitalization of 80/671 (11.9%). Multivariable logistic regression analysis showed that left ventricular ejection fraction (LVEF), fasting blood glucose, N-terminal pro-brain natriuretic peptide(NT-proBNP), and LCR were independent factors associated with the occurrence of CI-AKI in STEMI patients after PCI. RCS analysis revealed a linear dose-response relationship between LCR and CI-AKI. A traditional prediction model was established using LVEF, fasting blood glucose, and NT-proBNP. After incorporating LCR, a new predictive model was developed, and the results showed a significant improvement in the predictive performance of the new model for in-hospital CI-AKI in STEMI patients (NRI=0.383, 95%CI: 0.1949-0.5711, P<0.001; IDI=0.017, 95%CI: 0.0093-0.0244, P<0.001). Conclusions Low LCR is an independent risk factor for CI-AKI after PCI in STEMI patients. There is a linear dose-response relationship between LCR and CI-AKI. Incorporating LCR improves the predictive ability for the occurrence of CI-AKI.