This study aimed to explore the protective effect of hydrogen as an antioxidant on monocrotaline (MCT)-induced pulmonary hypertension (PH). Forty-eight SD rats were equally randomized into four groups: SHAM group, MCT group, MCT+Oral-H2 group and MCT+Inj-H2 group. The results showed that the mean pulmonary arterial pressure, right ventricle weight and right ventricular hypertrophy index in MCT group were significant higher than those in SHAM group; pulmonary inflammatory response, atrial natriuretic factor, 3-nitrityrosine and intercellular adhesion molecule-1 were also increased significantly in MCT group. These indexes were decreased significantly in both MCT+Oral-H2 group and MCT+Inj-H2 group, which indicate Oral-H2 and Inj-H2 have similar effects of preventing the development of PH and mitigating RV hypertrophy. The protective effect of hydrogen is associated with its antioxidative ability and action of reducing pulmonary inflammatory response. While Oral-H2 is more convenient than Inj-H2, Oral-H2 may be ideal for clinical use in future.