Abstract： Objective To investigate the role of cyclosporin A (CsA) in regulating the prolifera-tive capacity and apoptosis of cultured human peripheral blood endothelial progenitor cells (EPCs). Methods EPCs were obtained from cultured mononuclear cells isolated from peripheral blood of healthy adults, and stimulated with or without cyclosporin A (CsA, 10 mg/L). Cell proliferation and apoptosis were determined using the colorimetric method and terminal deoxyrmcleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining respectively. The expression of caspase-3, bcl2 and bax was assayed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. To deter-mine the effects of CsA at the different concentrations on EPCs proliferation, some cells were treated with CsA in a series of final concentrations (0, 10, 100, 500, 1000 and 10000 μg/L) for 48 h, and cell proliferative capacity was detected by the colorimetric method. Results Stimulation with 100 μg/L CsA markedly prevented EPCs proliferation, and the effects of CsA on EPCs proliferation were dose-dependent at the concentrations ranging from 10 μg/L to 10000 μg/L. Cells stimulated with CsA (10 mg/L) resulted in a decrease of numbers by both ways of preventing proliferation and promoting apoptosis. CsA significantly inhibited bcl2 gene expression and promoted caspase-3 gene expression, but it failed to alter the expression of bax gene. Conclusion CsA significantly decreases the prolifera-tive capacity of cultured human EPCs from peripheral blood.