Establishment of robust xenograft models is critical to studying human hematopoiesis in a physiologic setting. Using a recently developed immunodeficient mouse strain, we have established long-term multilineage human grafts and demonstrated their serially transplantability using limited numbers of purified human hematopoietic stem cells (HSCs). Herein, we describe our protocol for the isolation of human HSC (Lin-CD34+CD38−CD90+) from umbilical cord blood (CB) as well as the xenotransplantation system that allows stable engraftment of human hematopoietic cells with as few as ten HSCs. Isolation of CB mononuclear cells requires 2–3 h, and cells may be cryopreserved before transplantation. Isolation of HSC requires approximately 2–3 h, and transplantation requires 1 h. Short-term and long-term engraftment is assessed 4–6 weeks and 10–12 weeks post-transplantation, respectively, with preparation and analysis time requiring 4–8 h at each time point.