The transcription factor Meis1 is expressed preferentially in hematopoietic stem cells (HSCs) and overexpressed in certain leukemias. However, the functions of Meis1 in hematopoiesis remain largely unknown. In the present study, we found that Meis1 is required for the maintenance of hematopoiesis under stress and over the long term, whereas steady-state hematopoiesis was sustained in the absence of Meis1 in inducible knock-out mice. BM cells of Meis1-deficient mice showed reduced colony formation and contained significantly fewer numbers of long-term HSCs, which exhibited loss of quiescence. Further, we found that Meis1 deletion led to the accumulation of reactive oxygen species in HSCs and decreased expression of genes implicated in hypoxia response. Finally, reactive oxygen species scavenging by N-acetyl cysteine or stabilization of hypoxia signaling by knockdown of the von-Hippel-Lindau (VHL) protein led to reversal of the effects of Meis1 deletion. The results of the present study demonstrate that Meis1 protects and preserves HSCs by restricting oxidative metabolism.