Background: Neutrophil and albumin are respective indicators of inflammation and malnutrition. Whether combining those 2 markers can predict acute prognosis in patients with ST-segment elevation myocardial infarction (STEMI) remains unknown. This study aimed to investigate the prognostic value of neutrophil percentage to albumin ratio (NPAR) for in-hospital mortality in STEMI patients. Material/Methods: There were 1024 patients hospitalized with acute STEMI retrospectively enrolled in this study. Demographic, clinical, and admission laboratory data were extracted from medical record. NPAR was calculated as neutrophil percentage numerator divided by albumin in the admission blood samples. In-hospital mortality was designed as the primary outcome in the study, major adverse cardiac events (MACE) and cardiac death were recorded as the secondary clinical outcomes. Results: The rates of in-hospital mortality, MACE, and cardiac death in high NPAR group were significantly higher than those in the low NPAR group (P<0.001, P=0.004, P<0.001). The Kaplan-Meier analysis showed worse outcomes in higher NPAR group (P<0.001). NPAR levels and age independently predicted in-hospital mortality. A NPAR value >1.9 was identified as an effective cut point in STEMI for in-hospital mortality (P<0.001, sensitivity 82%, specificity 52%). Conclusions: Admission NPAR was independently correlated with in-hospital mortality in patients with STEMI.