To characterize the CD45RA+and CD45RO+T lymphocyte subsets in the peripheral blood of patients with cGVHD induced by allogeneic haematopoietic stem cell transplantation ( allo-HSCT ) and to explore their relations with the disease.Methods:The peripheral blood was collected from 64 patients after allo-HSCT,including 21 non-cGVHD patients,15 light grade cGVHD patients,18 mild grade cGVHD patients and 10 severe grade cGVHD patients,then CD4+CD45RA+,CD4+CD45RO+, CD8+CD45RA+and CD8+CD45RO+T lymphocyte subsets were detected by flow cytometry ( FCM).Results: Compared with the control,the percent of CD4+CD45RA+T lymphocyte in patients with light,mild and severe grade cGVHD decreased markedly (P<0.05),the percent of CD4+CD45RO+T lymphocyte increased markedly (P<0.05).But there were not obviously change in the patient with different grade cGVHD.The percent of CD8+CD45RA+,CD8+CD45RO+T lymphocyte did not change obviously.Conclusion:CD4+CD45RA+and CD4+CD45RO+may play an important role in the pathogenesis of cGVHD.