Objective To measure the level of circulating endothelial progenitor cells ( EPCs) in peripheral blood of patients with acute exacerbation of chronic obstructive pulmonary disease ( AECOPD) , and to explore the relationship between EPCs and severity markers of the disease and cardiovascular adverse outcome predictors.Methods Forty patients with COPD were recruited, including 27 at acute exacerbation phase and 13 with stable COPD from December 2010 to December 2011. Sixteen healthy nonsmokers were included as controls. Circulating EPCs were isolated by Ficoll density-gradient centrifugation and purified by Magnetic Activated Cell Sorting system. High-sensitivity C-reactive protein ( hsCRP) was estimated by using a latex immunoturbidimetric assay kit, and matrix metalloproteinase-9 ( MMP-9) was measured by enzymelinked immunosorbent assay ( ELISA) . Arterial blood gas analysis and echocardiograph were performed in the AECOPD patients. The correlations between circulating EPCs, lung function, and cardiovascular markers were investigated. Results Circulating EPCs were significantly lower in AECOPD and stable COPD patients compared with the healthy controls [ ( 5.1 ±2.6) ×103 /mL and ( 6.0 ±3.2) ×103 /mL vs. ( 9.0 ±4.3) × 103 /mL, Plt;0. 05] . EPCs had a weak correlation with hsCRP ( P = 0. 033) , but not with MMP-9. In the AECOPD patients, EPC counts were significantly inversely correlated with PASP ( pulmonary artery systolic pressure) and NT-proBNP ( amino-terminal pro-brain natriuretic peptide) levels, and positively with left ventricular ejection fraction. No correlations were found between EPCs and lung function, blood gas, hospital stays or smoking index. Conclusions Circulating EPCs were significantly lower in AECOPD patients compared with healthy controls, in which systemic inflammation might be involved. Decreased EPCs were correlated with cardiac dysfunction in patients with AECOPD, which may account for the increased cardiovascular risk in this population.