To improve the understanding of EB virus associated post-transplant lymphoproliferative disorder (EBV-PTLD) after allogeneic hematopoietic stem cell transplantation,and to explore the early diagnosis and treatment of EBV-PTLD.The clinical data of 2 cases of acute lymphoblastic leukemia patients who had EBV-PTLD after unrelated donor transplantation were reported.Both of them were pretreated with TBI+CTX+Flu+Ara-C+ATG (rabbit) before unrelated donor transplantation.EBV-DNA increment,fever and lymphadenectasis occurred on day 41th and day 67th after transplantation respectively.The two patients received the preemptive therapy of reduction of CsA and application of rituximab.All clinical symptoms were completely disappeared.Dynamic monitoring of EBV-DNA is important for patients with high risk factors of EBV-PTLD.The prognosis of EBV-PTLD can be improved by early application of rituximab and the reduction of immunosuppression.