BACKGROUND Benign prostatic hyperplasia (BPH) is a common urological condition in aging men. While dihydroartemisinin (DHA) exhibits a wide range of pharmacological activities, to date, there have been no studies examining the effects of DHA on BPH. METHODS An in vivo BPH model was constructed in rats via daily subcutaneous injection of testosterone propionate (TP) for 28 consecutive days. Rats were randomly distributed into four groups and treated as follows: (I) control; (II) TP treatment; (III) TP and finasteride treatment (positive control); and (IV) TP and DHA treatment. At the end of the experiment, rats were sacrificed and the prostate weight, prostate index, thickness of the epithelium, collagen deposition, serum dihydrotestosterone (DHT) levels, 5α-reductase 2 (5AR-2) expression, and proliferating cell nuclear antigen (PCNA) levels in the prostate were examined. Normal human prostatic epithelial RWPE-1 cells were used in in vitro experiments to further investigate the anti-proliferative effects of DHA. RESULTS TP increased the prostate weight and prostate index in rats, and this effect was reduced with DHA treatment. In addition, DHA attenuated the morphological changes and collagen deposition in the prostate tissue induced by TP. Furthermore, DHA reduced the expression of PCNA, serum DHT, and prostatic 5AR-2 in rats with TP-induced BPH. In vitro analysis revealed that DHA significantly inhibited the proliferation of TP-treated RWPE-1 cells. CONCLUSIONS DHA significantly inhibited the development of BPH by suppressing serum DHT levels, prostatic 5AR-2 expression, and the proliferation of benign prostatic epithelial cells. Thus, DHA is a novel medicinal agent with potential therapeutic efficacy in the treatment of patients with BPH.