Objective : In benign prostatic hyperplasia, dihydrotestosterone acts as a potent cellular androgen and promotes prostate growth. Inhibiting enzyme 5${alpha}$-reductase, which is involved in the conversion of testosterone to the active form dihydrotestosterone, reduces excessive prostate growth. Recently Scutellaria baicalensis has been related reports about the effect of baicalein on anti-proliferation of the prostate gland. In this study, we investigated the effects of Scutellaria baicalensis on cytopathological alterations and expression of 5${alpha}$-reductase in the rat model of benign prostatic hyperplasia induced by castration and testosterone treatment. Methods : Sprague-Dawley rat were treated with testosterone after castration for induction of experimental benign prostatic hyperplasia, which is similar to human benign prostatic hyperplasia in histopathological profiles. Scutellaria baicalensis as an experimental specimen, and finasteride as a positive control, were administered orally. The prostates were evaluated by histopathological changes, testosterone levels, and the expression of 5${alpha}$-reductase genes. Results : While prostates of control rats revealed severe acinar gland atrophy and stromal proliferation, the rats treated with Scutellaria baicalensis showed a diminished range of tissue damage. In the reverse transcription-polymerase chain reaction(RT-PCR) of 5${alpha}$-reductase genes. Scutellaria baicalensis inhibited the expression of 5${alpha}$-reductase genes. Conclusions : These findings suggest that Scutellaria baicalensis may protect glandular epithelial cells and also inhibit stromal proliferation in association with the suppression of 5${alpha}$-reductase. From theses results, we suggest that Scutellaria baicalensis could be a useful remedy agent for treating benign prostatic hyperplasia.