This study aimed to investigate the efficacy of bosentan in the treatment of severe pulmonary hypertension in a young female patient with mixed connective tissue disease (MCTD) associated with antiphospholipid syndrome. A 27-year-old woman presented with sudden onset of dyspnea. She had not experienced any dyspnea before this period, and she was known to have MCTD. Laboratory tests showed positive results for antinuclear antibodies, anti-RNP antibodies, anticardiolipin antibodies, beta(2)-glycoprotein I, and lupus anticoagulant. A complete echocardiographic study was performed demonstrating a pulmonary artery systolic pressure (PAPs) of 85 mmHg. Treatment with bosentan was initiated. After 12 days, the patient improved clinically. After 6 months of therapy, the follow-up echocardiography showed a near-normalization of PAPs. Patients who develop PAH secondary to an underlying systemic disease often have a poor survival rate. In this report, we describe a correlation between anticardiolipin antibodies and rapidly progressive pulmonary hypertension. Indeed, the patient in this study very likely improved secondary to the effect of bosentan which produces systemic and pulmonary vasodilatation associated with pulmonary vascular remodeling as well as possible antifibrotic, anti-inflammatory and antiatherothrombotic effects on cells of lungs damaged by an aPL-antibody mediated mechanism.