Background : Pulmonary vascular changes which occur early in the course of chronic obstructive pulmonary disease (COPD) are prevalent manifestation and later cause pulmonary hypertension, which is a bad prognostic factor in COPD. Beraprost sodium (BPS), an orally active prostacyclin analogue, has been shown to improve survival in patients with primary pulmonary hypertension. This study investigated the effect of BPS in the patients with COPD. Methods : This is a double-blind randomized placebo-controlled, two center clinical trial. Twenty one consecutive patients with COPD were enrolled from June 2003 to June 2004 (patients treated with BPS for 3 months, BPS group, n=11; those with placebo, placebo group, n=10). The baseline demographic, pulmonary function and hemodynamic data were not significantly different between two groups. Results : On echocardiographic examination, trans tricuspid valve pressure gradient has decreased significantly after 3 months with beraprost in the BPS group [17.7(${pm}11.4$) to 8.2(${pm}8.9$) mm Hg, p-value<0.05], while there was no significant change in the control group. Six-minute walking distance has decreased in the control group and increased in the BPS group, but there was no statistical significance. Conclusion : In patients with COPD oral administration of BPS reduced the pulmonary arterial pressure. The clinical significance of this finding, that is improving symptoms and natural course of the disease, needs further study.