High Gleason grade prostate carcinomas are aggressive, poorly differentiated tumors that exhibit diminished estrogen receptor β (ERβ) expression. We report that a key function of ERβ and its specific ligand 5α-androstane-3β,17β-diol (3β-adiol) is to maintain an epithelial phenotype and repress mesenchymal characteristics in prostate carcinoma. Stimuli (TGF-β and hypoxia) that induce an epithelial-mesenchymal transition (EMT) diminish ERβ expression, and loss of ERβ is sufficient to promote an EMT. The mechanism involves ERβ-mediated destabilization of HIF-1α and transcriptional repression of VEGF-A. The VEGF-A receptor neuropilin-1 drives the EMT by promoting Snail1 nuclear localization. Importantly, this mechanism is manifested in high Gleason grade cancers, which exhibit significantly more HIF-1α and VEGF expression, and Snail1 nuclear localization compared to low Gleason grade cancers.