Background: Both endothelial dysfunction and low circulating androgen levels predict cardiovascular disease in men. Endothelial function evaluation is commonly performed by measuring flow-mediated vasodilatation of the brachial artery. However, studies have suggested that compared with evaluation of large arteries, microvascular function evaluation of peripheral arteries is a better predictor of increased cardiovascular disease risks. Although circulating levels of androgens, such as testosterone and dehydroepiandrosterone sulfate (DHEA-S), positively correlate with cardiovascular function, the association between circulating androgen levels and microvascular function is unknown. In this study, we investigated whether serum androgen levels correlate with microvascular endothelial function in men. Methods: The study included 105 Japanese men (age 59 ± 1 years) in whom we measured serum testosterone and DHEA-S levels. The reactive hyperemia index (RHI) determined by the Endo-PAT system (finger plethysmography) was used to evaluate microvascular endothelial function. Results: Serum testosterone levels were significantly correlated with the RHI (r = 0.32, P < 0.01). The association between serum testosterone levels and the RHI remained significant even after adjustment for confounders, including age and body mass index (β = 0.31, P < 0.01). Notably, serum DHEA-S levels were not associated with the RHI (r = 0.01, n.s.). Conclusion: This study showed that serum testosterone levels were positively correlated with microvascular endothelial function in men. These results suggest that endogenous testosterone level is one of the determinants of microvascular endothelial function and may become a biomarker reflecting lifestyle modifications-induced improvement in cardiovascular function in men.