Benign prostatic hyperplasia (BPH) is an age-related disease of unknown etiology, characterized by prostatic enlargement coincident with distinct alterations in tissue histology. In the present study, we investigated whether triptolide can prevent testosterone-induced prostatic hyperplasia in rats. Castration was performed via the scrotal route after urethane aesthesia. BPH was induced in experimental groups by daily subcutaneous injections of testosterone propionate (TP) for two weeks. Triptolide was administered daily by oral gavage at a dose of 100 and 50 μg·kg −1 for 2 weeks, along with the TP injections. On day 14, the animals were humanely killed by cervical dislocation after aesthesia. Prostates were excised, weighed, and used for histological studies. Testosterone and dihydrotestosterone (DHT) levels in serum and prostate were measured. The results showed that triptolide significantly reduced the prostate weight, and the testosterone and DHT levels in both the serum and prostate. Histopathological examination also showed that triptolide treatment suppressed TP-induced prostatic hyperplasia. In conclusion, triptolide effectively inhibits the development of BPH induced by testosterone in a rat model.