Objective <p>Severe fever with thrombocytopenia syndrome (SFTS), caused by the novel Bunyavirus (NBV), is a tick-borne infectious disease associated with high morbidity and mortality. Currently, no effective treatment or vaccine exists for SFTS. Early identification of prognostic factors is crucial for clinical management. This study aimed to evaluate the prognostic value of the procalcitonin/albumin to urea nitrogen ratio (PAU) in SFTS patients.</p> Methods <p>This retrospective observational study enrolled 259 consecutive patients with SFTS admitted to Tongji Hospital from April 2023 to November 2024. Patients were stratified into survival (<i>n</i> = 172) and death (<i>n</i> = 87) groups based on clinical outcomes.</p> Results <p>Multivariable logistic regression identified advanced age, altered mental status (AMS), elevated PAU and high viral load as independent predictors of adverse outcome in SFTS. PAU exhibited strong discriminative performance (AUC 0.810; 95% CI 0.757–0.857; sensitivity 75.7%, specificity 73.0%), with an optimal cut-off of 0.06 µmol/L. Integration of PAU with age, viral load and AMS further improved accuracy (AUC 0.897; 95% CI 0.858–0.936). Bootstrap internal validation yielded a calibration curve closely approximating the diagonal, confirming robust predictive efficacy of the composite model.Kaplan-Meier analysis revealed significantly worse prognosis in high-PAU patients (<i>P</i> &lt; 0.001).The longitudinal trend analysis revealed an increasing trend in PAU among non-survivors, while survivors exhibited a decreasing trend.</p> Conclusion <p>PAU represents a novel composite biomarker that integrates inflammatory and organ dysfunction parameters, providing reliable prognostic prediction for SFTS patients.</p> Clinical trial number <p>Not applicable.</p>