MicroRNA (miRNA) are small non-coding RNA that act at the post-transcriptional level, regulating protein expression by repressing translation mRNA target. They can be detected in plants, animal species and viruses, and are involved in numerous cellular processes. MicroRNA-155 (miR-155) which is a kind of microRNAs expressed in hematopoietic cells. Recent data indicate that MiR-155 plays a key role in the pathogenesis of hematological malignancies through regulating cell signal transduction pathways of cell proliferation, differentiation and apoptosis, acting predominantly as an oncomir. MiR-155 may be an important indicator to assess the diagnosis, treatment and prognosis of patients with hematological malignancies, including malignant lymphoma, acute myeloid leukemia, and myelodysplastic syndrome. It could be suggested that drugs such as antisense oligonucleotides able to down-regulate miR-155 expression would provide a novel, and possibly specific way to control the growth of a range of haematopoietic malignancies in conjunction with classical cytotoxic therapy. The purpose of this review is to summarize current findings on the role of miR-155 in hematopoietic malignancies and, moreover, to highlight their role as potential therapeutic tools.