The protein, KRas, has an essential role in regulating cellular survival, proliferation and differentiation. Mutations in KRas cause blood system cancers in mice, but little is known about the effects of increased expression of normal KRas protein. We evaluated the blood system and blood stem cell content of mice that were engineered to have increased expression of normal KRas. We discovered that increased KRas protein promoted blood stem cell self-renewal and proliferation that was demonstrated when the stem cells were transplanted into recipient mice. However, after the stress of a second transplantation, the stem cells that overexpressed KRas were exhausted and lost their stem cell function. Finally, when mice were stressed with radiation exposure, the animals that had increased KRas protein displayed more rapid recovery of the blood system after injury compared to control mice. In summary, this study demonstrated that KRas protein strongly promotes blood stem cell growth and self-renewal, but at the expense of early exhaustion.