Objective To study the influence of Cramp gene knockout on the function of hematopoietic stem cell in aging. MethodsCells from the bone marrow of different age Cramp knockout and wild type mice were analyzed by flow cytometry. ResultsCompared with 12 months old wild type mice, percentage of long term hematopoietic stem cell decreased, multipotent hematopoietic progenitor increased; percentages of pre B and immature B cells decreased, and mature B cells increased in Cramp knockout mice. ConclusionCramp gene knockout plays an important role in hematopoietic stem cell and the development of B lymphocytes in aging.