Estrogen receptor alpha (ERa) is one of the major sub-types of estrogen receptors. ERa plays an important role in cellular proliferation and differentiation, chiefly in mammary tissues. In the present study we aimed to quantify of ERa mRNA and protein expression in breast tissues from the Iranian population using a real-time PCR assay. Twenty nine breast tissues including 19 adenocarcinomas and 10 normal controls were recruited from the Iranian population. mRNA extraction and cDNA synthesis were performed from these tissues using commercial kits. ERa mRNA and protein expression was quantified using real-time PCR and immunohistochemistry respectively. The results showed high expression of ERa mRNA (68%) and protein (53%) in the majority of breast cancer tissues compared to normal breast tissues (p= 0.035). Also, high ERa mRNA was associated with tumour size of breast carcinomas. In this study, we first reported the expression of ERa in Iranian patients with breast cancers and demonstrated prevalence of the expression to be similar to breast cancers noted in other populations.