Estrogens have been recently postulated as potential agents in the development and progression of prostate cancer. Previous studies have demonstrated presence of both variants of estrogen receptor (ER); ER alpha (ERα) and ER beta (ERβ) in differing proportions between normal prostate and prostate cancer. It has been previously suggested that estrogens may either accelerate or inhibit growth of prostate cancer cell growth, depending on ER status. In particular, ERβ is considered to have a growth inhibitory role in prostate tissue. ERβ is significantly expressed in human prostate cancer cells, and hence it is considered a key factor for anti-cancer therapy. Therefore, various types of ERβ ligands have been investigated to clarify the mechanism of ERβ-mediated pathway of inhibitory effects on prostate cancer cells. Herein, we review recent examinations of ERs in prostate cancer, and the significance of ER mediated signaling pathways, with a focus on ERβ as prospective therapeutic targets in prostate cancer.