Our results demonstrate that (a) the plasma SOD activity was markedly reduced in patients with IPAH compared to that in healthy subjects, (b) patients with BMPR2 mutation had a lower Ec-SOD level than the no-mutation subjects, (c) only Ec-SOD activity was correlated with hemodynamic abnormalities and survival, and (d) a decreased Ec-SOD activity was associated with an increased mortality risk, suggesting that the use of Ec-SOD may be superior to Cu/Zn-SOD or Mn-SOD for supplemental treatment if possible. Here, SOD2 is linked to idiopathic pulmonary arterial hypertension.