<p><b>OBJECTIVE</b>To explore the value of CD3CD4T cell count in prediction of viral infections after allogeneic hematopoietic stem cell transplantation(allo-HSCT) in the patients with severe aplastic anemia(SAA).</p><p><b>METHODS</b>A total of 78 SAA patients with allo-HSCT in Guangzhou First People's Hospital from January 2014 to July 2016 were enrolled in this study. The absolute numbers of CD3CD4T cells were measured by flow cytometry at 1,2,3,6, and 12 month after allo-HSCT. According to the cell counts, the patients were divided into 3 groups: i.e. <50/µl (n=120), 50-100/µl(n=48) and >100/µl(n=123)groups. The infection incidences of human cytomegalovirus (HCMV) and Epstein-Barr virus(EBV) within 2 weeks around each time point were compared between different groups. According the counts of CD3CD4T cells at 3 months after-transplant, these patients were divided into 2 groups, i.e.>100/µl (n=30) and ≤100/µl (n=48). The incidences and duration of HCMV and EBV infection, overall survival rate were compared between 2 groups.</p><p><b>RESULTS</b>The incidences of CMV and EBV infection significantly decreased in CD3CD4T cell >100/µl group as compared with <50/µl and 50-100/µl groups. At 3 months after-transplant, there was lower incidence rates of CMV disease, EBV infection, shorter durations of CMV infection and better survival in CD3CD4T cell >100/µl group as compared with ≤100/µl group.</p><p><b>CONCLUSION</b>CD3CD4T cell count is a good predictor for CMV and EBV infection after allo-HSCT in SAA patients. There are low risk of infe-ctions from CMV and EBV when CD3CD4T cell count >100/µl in any time after transplant, which means lower occurrence of CMV and EBV infection and better survival when CD3CD4T cell counts is >100/µl in 3 months after transplant in SAA patients.</p>