BACKGROUND: Finasteride and doxazosin are used for the treatment of benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). Epithelial-mesenchymal transition (EMT) plays an important role in BPH, little is known about the growth inhibition and anti-fibrosis effects of doxazosin on the regulation of EMT and morphology in the prostate. OBJECTIVES: The present study examined the effects of doxazosin on testosterone propionate (TP)-induced prostate growth in vivo and in vitro and its impact on the EMT and TGF-β/Smad signaling pathway. METHODS: Doxazosin (5 or 10 mg/kg) and finasteride (10 mg/kg) were administered orally for 28 days in TP-induced mice. The prostate index (prostate/body weight ratio), morphological characteristics and the protein expression of the prostate were examined. We further examined the effects of doxazosin and finasteride on the EMT and TGF-β/Smad signaling pathway in mice and in human prostate stroma cell (WPMY-1). RESULTS: The prostate wet weight, prostate index decreased after treatment. Doxazosin (5 or 10 mg/kg), finasteride (10 mg/kg) or a combination (doxazosin + finasteride) were shown to reverse the pathological and morphological characteristics of the prostate. Doxazosin and finasteride inhibited TP-induced prostate growth, EMT, and the TGF-β/Smad signaling pathway by downregulating the expression of TGF-β1, TGFBR2, p-Smad2/3, N-cadherin, vimentin, fibronectin and α-SMA, whereas expression of E-cadherin was increased after treatment with either doxazosin or finasteride. Doxazosin (1-50 μM) inhibited normal human prostate stroma cell growth (WPMY-1) after 48 h with or without testosterone treatment. Doxazosin also regulated the EMT and proteins related to the TGF-β/Smad signaling pathway in WPMY-1 cells after 24 h. Additionally, doxazosin decreased protein expression of the prostate specific antigen both in vivo and in vitro. CONCLUSION: This study demonstrated that doxazosin inhibits prostate growth by regulating the EMT and TGF-β/Smad signaling pathways in the prostate This finding suggests that doxazosin has potential as a new signaling pathway for the treatment of BPH.