The growth of prostate cancer is sensitive to androgen, and hormonal therapy has been used for treatment of advanced cancer. About 80% of prostate cancers initially respond to hormonal therapy, however, more than half of the responders gradually become resistant to this therapy. Changes in tumors from an androgen-responsive to an androgen-unresponsive state have been widely discussed. Since androgen action is mediated by androgen receptor (AR), abnormalities of AR is believed to play an important role of the loss of androgen responsiveness in prostate cancer. This article focused on the role of AR in the progression of prostate cancer.