Background: Circulating endothelial progenitor cells (EPCs) with an endothelial phenotype contribute to the regeneration and repair of the artery. The number of circulating EPCs has an inverse correlation with chronic smoking and endothelial dysfunction. Green tea cathechin improved endothelial dysfunction. However, the effect of green tea cathechin on the number of circulating EPCs and endothelial dysfunction in chronic smoker is not well-known. Methods: In 10 young healthy smokers (29.3짹2.1 years, male), endothelial function defined by flow-mediated endothelium dependent vasodilation (FMD) of the brachial artery via ultrasound, as well as the number of EPCs isolated from peripheral blood, were determined by baseline and 2 weeks after taking green tea (8g/day). Circulating EPCs were quantified by flow cytometry as CD45lowCD34+VEGFR2+ (EPCs) in 10 smokers and by acyl-LDL and lectin double positive cells after 7 days culture. Results: Changes of clinical characteristics, hsCRP and laboratory examination were not different between the baseline and after 2 weeks. EPC levels were inversely correlated with the number of cigarettes smoked. Circulating EPCs by flow cytometry (308.0짹240.2/ml vs 968.0짹405.3/ml, P<0.02) and cultured EPCs (107.5짹31.3/10 field vs 166.2짹56.0/10 field, P<0.002) increased rapidly after 2 weeks green tea medication. FMD was significantly improved after 2 weeks (4.99짹1.71 vs 7.74짹1.64, p<0.002). The FMD correlated with EPC count (r = 0.59, p<0.05). Conclusion: The number of circulating EPCs snd FMD was reduced in chronic smokers. Green tea led to a rapid improvement of EPC levels and FMD. Even short-term green tea may be an effective means to reduce cardiovascular risk in chronic smoker.