Background: Cardiovascular diseases (CVDs) are the main cause of mortality worldwide. The fact that men are more affected than women supports the hypothesis that testosterone is a risk factor of CVD. Endothelial progenitor cells (EPC) have an important role in vascular repair and angiogenesis. However, the effects of androgens on these cells are still unclear. In this study, we aimed to determine the effects of testosterone on the number of circulating EPCs. Methods: In this experimental study, 24 male Wistar rats were randomly allocated to four groups of six. The first group underwent sham operation and received 0.1 ml of subcutaneous sesame oil (as placebo) every day for three weeks. The other three groups underwent orchidectomy and received different concentrations of subcutaneous testosterone for three weeks. Finally, the number of EPCs was measured by flow cytometry. Findings: The number of circulating EPCs in the sham group decreased significantly. The number of EPCs in castrated groups that received 5 mg/kg/day testosterone increased significantly in comparison with castrated groups that received vehicle and 1 mg/kg/day testosterone (P < 0.05). Conclusion: Our findings suggest endogenous and exogenous testosterone to affect the number of circulating EPCs. Keywords: Endothelial progenitor cells, Testosterone