Objective:To explore the value of serum soluble growth stimulation expressed gene 2 (sST2) in predicting prognosis of patients with connective tissue disease-related pulmonary arterial hypertension (CTD-PAH).Methods:This retrospective cohort study enrolled 60 CTD-PAH patients diagnosed by right heart catheterization (RHC) during Jan 2017 and Jul 2022. Baseline and follow-up data collected including the levels of sST2, demographic data, clinical data of CTD and PAH, treatment regimen of CTD and PAH, survival status and the onset time of clinical deterioration events. The primary endpoint was the first occurring of clinical deterioration in 3-years. The t-test or Wilcoxon rank-sum test was used for continuous variables com-parison between different groups, and the chi-square test was used to compare categorical variables. Event-free survival rates were evaluated using Kaplan-Meier analysis and groups comparison were performed by the log-rank test. COX univariate and multivariate proportional hazard models were used to identify independent risk factors for poor prognosis. Results:Compared with the patients with sST2<35 ng/ml, CTD-PAH patients with sST2 ≥ 35 ng/ml showed higher WHO cardiac funcation class (Ⅲ-Ⅳ), mean right atrial pressure, N-terminal probrain na-triuretic peptide(NT-proBNP) and CRP levels[13/34 vs 19/26, χ2=7.19, P=0.007; 4.00(3.00, 6.00)mmHg vs 8.00(4.00, 12.00)mmHg, Z=-2.98, P=0.003; 474.30(135.70, 1 947.50) ng/L vs 2 650.50(485.33, 5 906.50)ng/L, Z=-2.72, P=0.007; 3.24(2.56,7.01)mg/L vs 9.66(3.20, 19.33)mg/L, Z=-2.50, P=0.012]; Kaplan-Meier analysis showed that event-free survival rate in 3 years was significantly lower in patients with sST2 ≥ 35 ng/ml (24.1% vs 84.0%, P=0.001). Multivariate COX regression analysis showed that sST2 was an independent predictor of clinical worsening in patients with CTD-PAH [ HR (95% CI)=1.020 (1.001, 1.039), P=0.035]. Conclu-sion:Serum sST2 is an independent risk factor for clinical deterioration in CTD-PAH patients.