We evaluated the benign prostatic hyperplasia (BPH) with Yacon pill, the preparation composed of Smallanthus sonchifolius, Torilis japonica and Acorus gramineus. A total of 45 rats were divided into five groups. One group was used as a control and the other groups received subcutaneous injections of testosterone for 4 weeks to induce BPH. Yacon pill extract (200 or 400 mg/kg) was administered daily for 4 weeks to two groups by oral gavage concurrently with testosterone. The rats euthanized, the prostate and body weights were recorded, and tissues were subjected to hormone assay. In addition, we investigated proliferating cell nuclear antigen (PCNA) expression in the prostate using immunoblotting. Rats with BPH showed significantly increased prostate weights, increased dihydrotestosterone (DHT) levels in the serum and increased PCNA expression in the prostate; however, Yacon pill extracts treated rats showed significant reduction of prostate weights, DHT levels and PCNA expression compared with the BPH group. Conclusively, Yacon pill showed the possibility as ameliorable agents of BPH symptoms.