Abstract： Background Serum uric acid (UA), the final product of purine degradation, has been proposed to be a marker for the severity and a possible predictor of mortality in patients with pulmonary arterial hypertension (PAH). The objectives of this study were to elucidate whether serum UA level correlates with the clinical features and the hemodynamic variables in Chinese patients with PAH and to compare the difference of the correlates in patients associated with different etiologies. Methods Serum UA was assessed in 228 patients with three types of PAH (idiopathic PAH (IPAH), congenital heart disease related PAH (CHD-PAH) and connective tissue disease related PAH (CTD-PAH)) together with other clinical features. After the individualized treatment for at least 6 months, the UA levels and clinical features were re-evaluated in 88 patients. Results Serum UA was significantly elevated in patients with PAH compared with age-matched control subjects ((350.40±108.73) μmol/L vs (266.91±81.38) μmol/L), P＜0.001). Serum UA negatively correlated with cardiac output and mixed venous saturation (SvO<,2>) in all three types of PAH (all P＜0.05), positively correlated with the size of right ventricle in IPAH (P=0.002) and CTD-PAH (P=0.013) patients and with pulmonary vascular resistance just in CTD-PAH patients (P=0.001). Serum UA significantly decreased from (365.80±120.46) μmol/L to (333.67±117.56) μmol/L in 88 patients (P=0.006) with vasodilator therapy for at least 6 months, accompanied with a reduction in pulmonary vascular resistance from (15.13±6.96) Woods unit to (12.00±5.04) Woods unit (P=0.001) and an increase in cardiac output from (2.63±0.98) L/min to (3.08±1.04) L/min (P=0.005). Conclusions Serum UA increases in proportion to the clinical severity of all the three types of PAH, especially the CTD-PAH had a stronger correlations compared with IPAH and CHD-PAH. The serum UA levels also could partly reflect the response to the treatment in patients with PAH.