Leukemia cells can carry a small subset of poorly differentiated cells, which are considered to be precursors of lymphoblasts, myeloblasts, or monoblasts. Thus these cells are also called leukemia stem cells (LSCs) because they are capable of instigating, maintaining and serially propagating leukemia in vivo, while retaining the ability to differentiate into committed progeny that lack these properties. Like hematopoietic stem cells (HSCs), LSCs possess the ability of self-renewal under a complex regulatory system. The recent discovery of microRNAs may shed new light on regulation of LSCs and leukemogenesis. As master gene regulators, microRNAs participate in these processes through coordinated work with key transcription factors required for hematopoiesis. Therefore, microRNAs could play a critical role in normal HSCs as well as LSCs. The purpose of this review is to provide updates on the role of microRNAs in HSCs and LSCs and to highlight their potential in differentiation therapy of leukemias.