Many studies have shown that epigenetic regulation of ERs (oestrogen receptors) plays a key role in the pathogenesis of leukaemia. In the present study, it was found that the methylated status of ERalpha-A might serve as an epigenetic biomarker of leukaemias. In this study, the protein expression and cell apoptosis, cycle, proliferation and viability with and without 5-aza-dC (5-aza-2'-deoxycytidine) were evaluated with Western blotting, 3H-TdR (3H-thymidine) incorporation, propidium iodide staining and Trypan Blue staining respectively. The protein expression of ERalpha was significantly enhanced in all leukaemic cell lines using treatment with the DNA demethylation reagent 5-aza-dC. However, no obvious change in the protein expression of ERbeta takes place with 5-aza-dC. And with 5-aza-dC, cell apoptosis, cell cycle, cell proliferation and viability were all inhibited significantly. We also tracked 40 cases of leukaemias with ERalpha-A methylation (95%; 38 of 40) to observe the prognosis 1 year after chemotherapy treatment. The patients with ERalpha-A methylation have no obvious symptomatic relief; however, two patients without ERalpha-A methylation have obtained effective relief. This result suggested that ERalpha plays a significant role in leukaemogenesis, and the methylated status of ERalpha-A not only might serve as an epigenetic biomarker of leukaemias for diagnosis, but also has the potential to serve as a predictor of prognosis in leukaemias.