This study was conducted to investigate the effect of a corn silk extract on improving benign prostatic hyperplasia (BPH). The experimental animals, 6-week-old male Wistar rats, were divided into sham-operated control (Sham) and experimental groups. The experimental group, which underwent orchiectomy and received subcutaneous injection of 10 mg/kg of testosterone propionate to induce BPH, was divided into a Testo Only group that received only testosterone, a Testo+Fina group that received testosterone and 5 mg/kg finasteride, a Testo+CSE10 group that received testosterone and 10 mg/kg of corn silk extract, and a Testo+CSE100 group that received testosterone and 100 mg/kg of corn silk extract. Prostate weight and concentrations of dihydrotestosterone (DHT), 5α-reductase 2 (5α-R2), and prostate specific antigen (PSA) in serum or prostate tissue were determined. The mRNA expressions of 5α-R2 and proliferating cell nuclear antigen (PCNA) in prostate tissue were also measured. Compared to the Sham group, prostate weight was significantly higher in the Testo Only group and decreased significantly in the Testo+Fina, Testo+CSE10, and Testo+CSE100 groups (P < 0.05), results that were consistent with those for serum DHT concentrations. The concentrations of 5α-R2 in serum and prostate as well as the mRNA expression of 5α-R2 in prostate were significantly lower in the Testo+Fina, Testo+CSE10, and Testo+CSE100 groups than that in the Testo Only group (P < 0.05). Similarly, the concentrations of PSA in serum and prostate were significantly lower in the Testo+Fina, Testo+CSE10, and Testo+CSE100 groups (P < 0.05) than in the Testo Only group. The mRNA expression of PCNA in prostate dose-independently decreased in the Testo+CSE-treated groups (P < 0.05). BPH was induced through injection of testosterone, and corn silk extract treatment improved BPH symptoms by inhibiting the mRNA expression of 5α-R2 and decreasing the amount of 5α-R2, DHT, and PSA in serum and prostate tissue.