EGFR/MAPK signaling can induce a switch in MCF-7 breast cancer cells, from an ER-positive, Luminal-A phenotype, to an ER-negative, Basal-like phenotype. Although mechanisms for this switch remain obscure, Basal-like cancers are typically high grade and confer a poorer clinical prognosis. We previously reported that miR-206 and ER repress each other's expression in MCF-7 cells in a double-negative feedback loop. We show herein that miR-206 coordinately targets mRNAs encoding the co-activator proteins SRC-1 and SRC-3, and the transcription factor GATA-3, all of which contribute to estrogenic signaling and a Luminal-A phenotype. Overexpression of miR-206 repressed estrogen-mediated responses in MCF-7 cells, even in the presence of ER encoded by an mRNA lacking a 3' UTR, suggesting miR-206 affects estrogen signaling by targeting mRNAs encoding ER-associated co-regulatory proteins. Furthermore, EGF treatments enhanced miR-206 levels in MCF-7 cells and ER-negative, EGFR-positive MDA-MB-231 cells, while EGFR siRNA, or PD153035, an EGFR inhibitor, or U0126, a MAPK kinase (MEK) inhibitor, significantly reduced miR-206 levels in MDA-MB-231 cells. Blocking EGF-induced enhancement of miR-206 with antagomiR-206 abrogated the EGF inhibitory effect on ER, SRC-1 and SRC-3 levels, and on ERE-luciferase activity, indicating that EGFR signaling represses estrogenic responses in MCF-7 cells by enhancing miR-206 activity. Elevated miR-206 levels in MCF-7 cells ultimately resulted in reduced cell proliferation, enhanced apoptosis, and reduced expression of multiple estrogen-responsive genes. In conclusion, miR-206 contributes to EGFR-mediated abrogation of estrogenic responses in MCF-7 cells, contributes to a Luminal-A to Basal-like phenotypic switch, and may be a measure of EGFR-response within Basal-like breast tumors.