Eucommia ulmoides Oliver is known as an herbal medicine. Recently, Eucommia ulmoides oliver leaf extract (ELE) has been shown to improve vascular function and vascular hypertrophy in SHR. Pulmonary arterial hypertension (PAH) is a severe and progressive disease that causes right heart failure. The pathogenesis of PAH is generally characterized by persistent high pulmonary arterial resistance and pulmonary arterial remodeling. In the present study, we investigated the effects of ELE on hypoxia-induced PAH in mice. 10-weeks-old male C57BL/6J mice were orally administered a 5% ELE during exposure to hypoxia for 4 weeks. ELE significantly suppressed the elevation of right ventricular systolic pressure in hypoxia-induced PAH mice. In addition, hypoxia-induced pulmonary arterial muscularization was tended to be attenuated in ELE-treated mice. Our findings suggest that ELE may effectively improve the development of hypoxia-induced PAH by preventing the hypercontraction and/or vascular remodeling of pulmonary artery.