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 this study, we investigated the effects of Eucommia ulmoides oliver leaf extract (ELE) on hypoxia-induced PAH in mice. We observed that Eucommia ulmoides oliver leaf extract (ELE) improve right ventricular systolic pressure (RVSP) and pulmonary vessel muscularization. To identify an active ingredient, geniposidic acid (～1 mg/kg, ～5 mg/kg), a major component of ELE, were orally administered to C57BL/6J mice during exposure to hypoxia for 4 weeks. Geniposidic acid significantly suppressed the elevation of RVSP in hypoxia-induced PAH mice. In addition, hypoxia-induced pulmonary arterial muscularization was slightly attenuated in geniposidic acid-treated mice. In human pulmonary artery smooth muscle cells (HPASMC), endothelin-1-induced intracellular Ca²⁺ elevation was attenuated by geniposidic acid (200 µM). Furthermore, geniposidic acid (50 – 200 µM) increased the maximal respiration in HPASMC. These findings suggest that geniposidic acid may be active ingredient of ELE which effectively improve the development of hypoxia-induced PAH by preventing the vascular remodeling and mitochondrial dysfunction of pulmonary artery.