Resistance to chemotherapy treatment, which may lead to limited efficacy of systemic therapy in breast cancer patients, is multifactorial. Among the mechanisms of resistance to chemotherapy treatment, there are those closely related to estrogen receptor α, P-glycoprotein, multidrug resistance-related protein, glutathione S-transferase pi and topoisomerase-II. ERα is ligand-activated transcription factor that regulates gene expression and plays a critical role in endocrine signaling. In previous preclinical and clinical studies, positive ERα expression in breast cancer cells was correlated with decreased sensitivity to chemotherapy. This article reviews current knowledge on the predictive value of ERα with regard to response to chemotherapy. Better understanding of its role may facilitate patient selection of therapeutic regimens and lead to optimal clinical outcomes.