The 30% EtOH extracts of Ganoderma lucidum Fr. Karst (Ganodermateceae) showed weak 5alpha-reductase inhibitory activity and binding ability to androgen receptor. When LNCaP (lymph-node carcinoma of the prostate) cells were treated with the EtOH extracts, cell proliferation was inhibited. Treatment with the extracts significantly inhibited the testosterone-induced growth of the ventral prostate in castrated rats. These results showed that G. lucidum might be a useful ingredient in the treatment of androgen-induced diseases, such as benign prostatic hyperplasia or prostate cancer. From the 30% EtOH extracts, we isolated ganoderiol F, which showed binding activity to androgen receptor and inhibited LNCaP cell proliferation, as one of the active compounds in the 30% EtOH extracts.