We examined the effects of losartan, an angiotensin II type 1 receptor blocker, on prostatic hyperplasia in spontaneously hypertensive rats (SHRs). Thirty-six-old male SHRs were perorally treated with losartan (3 or 10 mg/kg) or vehicle once daily for 18 weeks. Wistar Kyoto rats (WKYs) were used as vehicle-treated controls. After the treatment, prostate weight, blood pressure, and prostatic blood flow were measured. The tissue malondialdehyde (MDA), interleukin-6 (IL-6), and basic fibroblast growth factor (bFGF) levels were measured. Histological analysis for the ventral prostate was performed by hematoxylin and eosin staining. Compared to the WKYs, the SHRs had significantly higher prostate weight, prostate weight/body weight ratio (PBR), blood pressure, glandular epithelial area, and tissue MDA, IL-6 and bFGF levels in the ventral prostate and lower prostatic blood flow. Treatment with losartan dose dependently caused recovery of prostatic blood flow and decreased PBR, blood pressure, glandular epithelial area, and tissue MDA, IL-6, and bFGF levels in SHRs. Chronic losartan treatment could improve the prostatic hyperplasia via recovery of reduction in prostatic blood flow in ventral prostate in SHRs.