Objective To investigate the efficacy, safety and tolerance of bosentan, a dual endothelin receptor antagonist, in Chinese patients with idiopathic pulmonary arterial hypertension (IPAH).Methods Totally 79 IPAH patients (hemodynamic criteria confirmed by right heart catheterization) were included in this open-label, prospective multicenter study. Patients received 62. 5 mg of bosentan twice daily for the first 4 weeks, and then up-titrated to 125 mg twice daily for another 12 weeks. The primary end point was the change in exercise capacity showed by six-minute walk distance (6MWD) from baseline to 16 weeks. Secondary end points included the change in World Health Organization (WHO) functional class,Borg dyspnoea scale and systolic pulmonary artery pressure measured by echocardiography. Results The 6MWD increased from (343. 7 ± 93.7) meters at baseline to (397.5 ± 104. 4) meters after 16 weeks ( P ＜0. 01 ), WHO functional class and Borg dyspnoea scale were also significantly improved after 16 weeks therapy compared to baseline levels (all P ＜0. 01 ). Furthermore, the systolic pulmonary artery pressure was significantly decreased from (97.8±25.2) mm Hg (1 mm Hg=0. 133 kPa) to (92.8 ±29.5) mm Hg (P ＜0. 05) after 16 weeks bosentan treatment. There was no patient withdrawal from this study for safety consideration. Conclusion Bosentan therapy is well tolerated and can improve the exercise capacity and WHO functional class in Chinese IPAH patients.