(IP) is used in traditional medicine and contains pharmacologically active compounds. However, the effect for BPH progression has not been elucidated. We herein examined the protective potential of IP extract on a testosterone-induced model of BPH in rats. To generate the BPH model, daily subcutaneous administration of testosterone was applied for 4 weeks. During this period, the rats were also administered a daily oral gavage of IP (150 mg/kg), finasteride (positive control), or vehicle. Testosterone treatment was associated with a significantly higher prostate-to-body weight ratio, serum dihydrotestosterone (DHT) level, and prostatic gene expression of 5α-reductase compared to untreated controls. Notably, IP plus testosterone co-treatment was associated with decreased epithelial thickness, down-regulation of proliferating cell nuclear antigen (PCNA) and cyclin D1, and upregulation of pro-apoptotic signaling molecules. IP co-treatment also down-regulated pro-inflammatory cytokines, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) and decreased inflammatory cell infiltration compared to the levels seen in the testosterone-induced BPH. IP appears to protect rats against the progression of testosterone-induced BPH by alleviating prostate cell growth and inflammatory responses, and thus may have potential for clinical use against BPH progression.