Summary Background Icariin is a major flavonoid isolated from Epimedium spp. leaves (Epimedium Herba), and has multiple pharmacological functions, including anti‐angiogenesis, anti‐oxidant, anti‐inflammatory and immunoprotective effects. Aim To investigate whether icariin can stimulate growth of hair follicles in mice and the underlying mechanism. Methods In vitro, the effect of icariin on hair growth was assessed by using a vibrissae hair follicle (VHF) organ‐culture model. The proliferation of hair matrix keratinocytes and the expression of insulin‐like growth factor (IGF)‐1 in follicles were examined by double immunostaining for 5‐bromo‐2′‐deoxyuridine and IGF‐1, in the presence or absence of icariin. Dermal papilla cells (DPCs) were cultured and IGF‐1 level was measured by reverse transcription‐PCR and ELISA after icariin treatment. In vivo, the effect of icariin on hair growth was examined by gavage feeding of icariin to mice whose backs had been depilated, and the conversion of telogen to anagen hair was observed. Results Treatment with icariin promoted hair shaft elongation, prolonged the hair cycle growth phase (anagen) in cultured VHFs, and accelerated transition of hair cycle from telogen to anagen phase in the dorsal skin of mice. There was significant proliferation of matrix keratinocytes and an increased level of IGF‐1 in cultured VHFs. Moreover, icariin treatment upregulated IGF‐1 mRNA expression in DPCs and increased IGF‐1 protein content in the conditioned medium of DPCs. Conclusions These results suggest that icariin can promote mouse hair follicle growth via stimulation of IGF‐1 expression in DPCs.