Pulmonary arterial hypertension (PAH) is a frequent complication in patients with systemic sclerosis. Bosentan is used in patients with symptomatic PAH; however, it has not been established whether or not bosentan ameliorates the progression of PAH in patients with no PAH-related symptoms. We present a case of systemic sclerosis with no PAH-related symptoms in which bosentan ameliorated exercise-induced PAH evaluated by 6-minute walk stress echocardiography, brachial flow-mediated dilation, and skin temperature of hands and feet. The results suggest that administration of bosentan in patients with early-stage PAH ameliorates pulmonary arterial vasodilatation through improvement of endothelial function.