Objective: To assess the effects of bosentan on Raynaud’s phemonenon and the skin temperature of hands and feet in patients with connective tissue diseases (CTDs) complicated with digital ulcers or pulmonary arterial hypertension (PAH). Methods: An open-label, non-controlled, single-center, prospective study, which was designed to exclude the seasonal bias. Bosentan was commenced from 62.5mg twice daily for four to six weeks, followed by 125mg twice daily for 10 to 12 weeks (total period was 16 weeks). Bosentan was reduced or discontinued if adverse events were appearing. Patients without adverse events for 16 weeks continued the trial for 52 weeks. Results: In 13 enrolled patients, six were patients with suspected PAH and eight had digital ulcers. Ten patients were diagnosed with systemic sclerosis (eight with limited cutaneous and two with diffuse cutaneous form), two with mixed connective tissue disease and one with systemic sclerosis (diffuse cutaneous form)-polymyositis overlap syndrome.