The NF-κB family of transcription factors are essential for different stages of murine haemopoiesis as supported by studies on single or double knockout mice. The function of NF-κB1 and NF-κB2 in haemopoietic stem cells (HSCs) has never been described before. In mice, the bone marrow c-Kit+Sca1+Lin- (KSL) population represent HSCs that have the ability to repopulate the bone marrow of lethally irradiated animals. Using knockout mice technology we were able to study the function of NF-κB1 and NF-κB2 in HSCs by performing amongst others transplantation assays, which is the most precise way to test HSC potential. Nfκb1-/- KSL cells are fully able to reconstitute lethally irradiated recipients indicating that the in vivo self-renewal capacity is unaffected. In contrast, colony assays showed NF-κB1 dependency. Upon serial replating, knockout cells were not able to form colonies and lost their in vitro self-renewal capacity. Transplantation of the nfκb2-/- KSL cells engraft with a proliferative phenotype and a competitive advantage, with changes in the B-cell and myeloid cell lineages. Similar to nfκb1-/-, nfκb2-/- KSL cells lose their function as stem cells upon serial replating. These findings highlight the importance of NF-κB family proteins in HSCs, especially NF-κB2 and should be considered in the development of future cancer treatment that target NF-B proteins.