Enhancer of zeste homolog 2 (EZH2), the core component of the polycomb group complex, plays a major role in normal hematopoiesis. The molecular function of EZH2 is to establish H3K27me3 mark on specific genes by which promotes transcriptional repression of target genes. The activity of EZH2 affects the balance between self-renewal and differentiation of hematopoietic stem cells. In addition, EZH2 contributes to the cell cycle regulation in mature lymphocytes. A large number of studies have been performed to identify the implication of EZH2 in tumor development of leukemia. Aberrant expression of EZH2 is increasingly recognized in leukemic malignancies. To clarify its therapeutic potential in hematopoietic malignancies it should be determined whether EZH2 is involved in the pathology of these neoplasms. This paper reviews the current knowledge of the role of EZH2 in the pathogenesis of myeloid and lymphoid leukemia. We will discuss the mechanisms in which microRNAs regulate the expression of EZH2 in different types of leukemias that may provide a means to alter cancer epigenetics associated to tumorogenesis to achieve therapeutic benefits.