Contrast-induced nephropathy (CIN) is a significant complication in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI). The role of the stress hyperglycemia ratio (SHR) as a predictor of CIN and mortality in these patients remains unclear and warrants investigation.To assess the relationship between SHR and CIN, as well as its impact on short-term mortality in ACS patients undergoing PCI.We conducted a retrospective cohort study using the MIMIC-IV database, including 552 ACS patients. SHR was calculated as the ratio of admission glucose to estimated average glucose from hemoglobin A1c. CIN was defined as a ≥ 0.5 mg/dL or ≥ 25% increase in serum creatinine within 48 h of PCI. Logistic regression and spline models were used to analyze the association between SHR and CIN, while Kaplan-Meier curves assessed 30-day mortality.Higher SHR levels were independently associated with increased CIN risk (OR 2.36, 95% CI: 1.56-3.57, P < 0.0001). A J-shaped relationship was observed, with CIN risk rising sharply when SHR exceeded 1.06. SHR was also a predictor of higher 30-day mortality (P < 0.0001). Subgroup analysis revealed a stronger SHR-CIN association in non-diabetic patients.SHR is an independent predictor of CIN and short-term mortality in ACS patients undergoing PCI. It offers potential for risk stratification and clinical decision-making, especially in non-diabetic patients.© 2025. The Author(s).