Objective To study the effect of Huangqi （Radix Astragali seu Hedysari） on the proliferation and cell cycle of endothelial progenitor cells （EPCs） of human peripheral blood. Methods The mononuclear cells were isolated from human peripheral blood by density gradient centrifugation. After 7 days’ culture

the anchorage-dependent cells were collected and the Huangqi Injectio （0.2

2

20 and 200mg/ml） was injected for intervention （for 6

12

24 and 48h）. The laser scanning confocal microscope was used to determine the EPCs of human peripheral blood

the methyl thiazolyl tetrazoliym （MTT） assay was applied to test the proliferation of EPCs in vitro

and the flow cytometry （FCM） was adopted to detect the changes of cell cycle. Results Huangqi promoted the proliferation of EPCs remarkably

showing a time- and dose-effect relation. The FCM analysis showed that the S-phase and G2/M-phase rate increased but G0/G1-phase rate decreased relatively （P<0.01）. Conclusion Huangqi functions to promote the proliferation of EPCs remarkably and its mechanism may be promoting DNA synthesis and increasing the number of cells entering S-phase.