Spinasterol, a biologically active compound, exhibits a number of pharmacological activities, including antitumor, antiulcerogenic and anticarcinogenic activity, and originates from the aerial parts of Aster scaber Thunb (Asteraceae). The present study investigated whether α-spinasterol isolated from Melandrium firmum Rohrbach could prevent benign prostatic hyperplasia (BPH) induced by testosterone propionate (TP) in rats. Male Wistar rats were randomly divided into four groups of eight rats following castration. A negative control group received subcutaneous injections of corn oil. Treatments were administered orally 1 h prior to TP injection. All the rats were sacrificed at the scheduled termination time and their prostates were removed, cleaned and weighed. The prostate size ratio (prostate weight/rat body weight) was then calculated. Additional histopathological examinations were conducted, and the levels of TP and dihydrotestosterone (DHT) in the serum and prostate were measured. TP significantly increased the prostate size ratio (P<0.01), and DHT and testosterone levels in the serum and prostate. The TP-induced increase was significantly inhibited in α-spinasterol-treated rats when compared with the negative controls (P<0.05). In addition, histopathological examination demonstrated that α-spinasterol treatment suppressed TP-induced prostatic hyperplasia. It is concluded that α-spinasterol can prevent TP-induced prostatic hyperplasia and may be beneficial in the management of BPH.