Objective To investigate the effects of Icariin on the androgen receptor signaling pathway in orthotopic transplanted tumor of SCID mice with prostate cancer. Methods Sixty?four male SCID mice were randomly divided into a model group and experimental groups A, B, and C, and subjected to intraprostatic injection of a human prostate cancer cell line (LNCaP) suspension to establish a prostate cancer orthotopic transplantation tumor model. After modeling for 2 weeks, experimental groups A, B, and C were gavaged by doses of 10, 40, and 80 mg/ kg, respectively, for 5 weeks, while the model group was administered saline for comparison. RT?PCR was used to detect androgen receptor (androgen receptor, AR) and expression of tensin homolog deleted on the tenth chromosome (phosphatase and tensin homolog phosphatase gene deleted on chromosome ten, PTEN). Western blotting was used to detect the specificity of a prostate cancer antigen (prostate?specific antigen, PSA) and phosphorylated AR (p?AR). Flow cytometry was used to characterize the cell cycle of LNCaP prostate cancer cells. Results After treatment, the expression levels of AR, p?AR, and AR mRNA were higher in the model group, while the expression of PTEN mRNA was low. The tumor inhibition rate of the model group was lower, and there was no significant difference between the tumor mass and the tumor volume before and after treatment ( P > 0. 05). In groups B and C after treatment, the inhibition rates were(42. 53 ±5. 72)% and(44. 81 ±4. 76)%, AR, p?AR, and PSA mRNA had low expression, and PTEN mRNA had high expression. Moreover, the proportion of cells in G0 / G1 phase decreased, the proportion of cells in S phase increased, and the proliferation of tumor cells was arrested in S phase, when compared with those in the model group, before and after treatment ( P < 0. 05). Conclusions Icariin may inhibit the proliferation of prostate cancer LNCaP cells by inhibiting the phosphorylation of AR, enhancing the expression of PTEN, and blocking the proliferation of tumor cells in the S phase.