To analyze the relation of early immune reconstitution with acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation (all-HSCT), the changes of CD3(+), CD4(+), CD8(+), CD25(+) and CD69(+) cells in peripheral blood from 26 patients with hematologic malignancies were assayed by flow cytometry within 2 months after allo-HSCT. All patients achieved hematopoietic reconstitution, and grade I and II - IV GVHD were developed in 9 and 5 patients, respectively. CD25(+) cells were increased in patients aGVHD at week 2 after transplantation and the peak value was appeared at week 3. The increase of CD25(+) cells was preceded the occurence of clinical signs of aGVHD. The maximal levels of CD25(+) cells increase correlated significantly with the severity of aGVHD. The increase of CD25(+) cells was declined along with remission of aGVHD signs. Our results suggest that analyzing immune reconstitution after allo-HSCT could predict occurence of aGVHD, and CD25(+) cell increase prior occurence of aGVHD is predictive marker for aGVHD.