Chronic hypoxia contributes to pulmonary hypertension through complex mechanisms that include enhanced NADPH oxidase expression and reactive oxygen species (ROS) generation in the lung. Stimulation of peroxisome proliferator–activated receptor γ (PPARγ) reduces the expression and activity of NADPH oxidase. Therefore, we hypothesized that activating PPARγ with rosiglitazone would attenuate chronic hypoxia–induced pulmonary hypertension, in part, through suppressing NADPH oxidase–derived ROS that stimulate proliferative signaling pathways. Male C57Bl/6 mice were exposed to chronic hypoxia (CH, Fi_O2 10%) or room air for 3 or 5 weeks. During the last 10 days of exposure, each animal was treated daily by gavage with either the PPARγ ligand, rosiglitazone (10 mg/kg/d) or with an equal volume of vehicle. CH increased: (1) right ventricular systolic pressure (RVSP), (2) right ventricle weight, (3) thickness of the walls of small pulmonary vessels, (4) superoxide production and Nox4 expression in the lung, and (5) platelet-derived growth factor receptor β (PDGFRβ) expression and activity and reduced phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression. Treatment with rosiglitazone prevented the development of pulmonary hypertension at 3 weeks; reversed established pulmonary hypertension at 5 weeks; and attenuated CH-stimulated Nox4 expression and superoxide production, PDGFRβ activation, and reductions in PTEN expression. Rosiglitazone also attenuated hypoxia-induced increases in Nox4 expression in pulmonary endothelial cells in vitro despite hypoxia-induced reductions in PPARγ expression. Collectively, these findings indicate that PPARγ ligands attenuated hypoxia-induced pulmonary vascular remodeling and hypertension by suppressing oxidative and proliferative signals providing novel insights for mechanisms underlying therapeutic effects of PPARγ activation in pulmonary hypertension.