Objective To explore the damaging effect of X-ray whole body irradiation on hematopoiesis andimmune functions in KKAy mice with type 2 diabetes mellitus. Methods KKAy mice were exposed to 4 Gy total bodyirradiation (TBI) ,and compared with C57BL/6J mice. All mice were euthanized for routine analysis of peripheral blood,hematopoietic progenitor cells (HPC), hematopoietic stem cells (HSC), and long-term hematopoietic stem cells (LTHSC)frequencies and the percentages of splenic lymphocytes and thymic lymphocytes. The function of HPCs was measuredby colony-forming unit-granulocyte and macrophage (CFU-GM) assay. Results The frequency of HSCs and LT-HSCs inKKAy mice was lower than that in C57 mice. After 4 Gy whole body irradiation, the percentages of WBCs, RBCs, PLTs,HG B and LYM% in peripheral blood of KKAy mice were decreased by 68. 42%, 12. 17%, 8. 78%, 30. 12%, and70. 84%, respectively. The percentages of HPCs, HSCs and LT-HSCs in bone marrow were decreased by 34. 02%,29. 49%, 35. 74%, respectively. The proportions of splenic B and T cells were decreased by 57. 85% and 58. 81%,respectively. The proportion of thymic CD4+ / CD8+ cells was decreased by 51. 7%. The HPC function (CFU-GM) was alsoimpaired. The decrease levels of bone marrow HSC, LT-HSC, peripheral blood RBC and HGB in KKAy mice weresignificantly lower than those in C57 mice.Conclusions Whole body irradiation by 4 Gy X-rays impairs the hematopoiesis and immune functions, and KKAy mice might show a greater tolerance to ionizing radiation than C57 mice.