Leukemia is the most common hematological malignancy, characterized by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow. Although impressive biologic advance has increased understanding of leukemogenesis, we know little regarding the pathogenic events leading to the initiation and progression of this disease. microRNAs (miRNAs) are now recognized as a class of small, non-protein-coding RNA molecules that can regulate the expression of many genes. The evolutionarily conserved small molecules play important roles in cellular development and function, through mediation of target gene repression. There is significant evidence showing that miRNAs play an important role in disease, especially in oncogenesis. Aberrant expression of miRNAs appears to be a common feature of haematological malignancies. Since the discovery of miR-15 and miR-16 in CLL, much effect has been done to investigate the small molecule in leukemia. Several research groups have shown differences in miRNA expression between normal and malignant cells in leukemia. So miRNAs may be involved in leukemia pathogenesis. Despite the recognition of their synthesis, we know little about their exact molecular function and the identifications of their target genes. Some targets of miRNAs are antiapoptotic genes such as Bcl2 and Tcl1. MiRNAs to these genes are natural antagonists and may be also applied in leukemia therapy. This article reviews the common science supporting miRNAs and their potential target genes in leukemia pathogenesis.