Hematopoietic stem cells (HSCs) are the key elements responsible for maintaining blood-cell production throughout life and for lymphohematopoietic reconstitution following bone marrow (BM) transplantation. Enhancement of the engrafting potential and expansion capabilities of HSCs as well as hematopoietic progenitor cells (HPCs) has been a long-time desire as a means of reducing the risks and difficulties that accompany BM transplantation. The ability of HSCs/HPCs to reconstitute the hematopoietic system of irradiated hosts is negatively regulated by an intracellular adaptor protein, Lnk. Here we have identified the functional domains of Lnk and developed a dominant-negative (DN) Lnk mutant that inhibits the functions of Lnk endogenously expressed in the HSCs/HPCs and thereby potentiates the HSCs/HPCs for engraftment. Importantly, even transient expression of DN-Lnk in HSCs/HPCs facilitated their engraftment under nonmyeloablative conditions and fully reconstituted the lymphoid compartments of immunodeficient host animals. HPCs expressing DN-Lnk were efficiently trapped by immobilized vascular cell adhesion molecule-1 (VCAM-1) in a transwell migration assay, suggesting involvement of Lnk in the regulation of cell mobility or cellular interaction in microenvironments. Transient inhibition of Lnk or Lnk-mediated pathways could be a potent approach to augment engraftment of HSCs/HPCs without obvious side effects.