The study was aimed to investigate the mobilization effect of medium dose of granulocyte colony stimulating factor (G-CSF) in allogeneic peripheral stem cell transplantation and changes of T lymphocyte subgroup in PBMNC before and after mobilization. G-CSF was administered at 600 microg/d (i.e. 300 microg i.v. twice a day) for successive 5 days to 31 matched sibling or unrelated donors for the mobilization. Stem cells were harvested on the fourth day. FACS was used to analyze the NC, MNC and T lymphocyte subgroups. The results showed that the number of NC, MNC, CD34(+) cells and CFU-GM in dose of 600microg/d significantly increased (P < 0.05), compared with 300 microg/d; the time for hematological reconstruction was significantly shortened (P < 0.05); the ratio of adverse effects was not obviously increased (P > 0.05) and the median percentage of CD3(+) lymphocytes before mobilization was 46.96% [(32.36-57.45)%], but 40.94% [(25.31-48.9)%] after mobilization, while the ratio of CD4(+)/CD8(+) did not significantly changed. It is concluded that the administration of G-CSF 600 microg/d in allo-PBSCT has a good effect in the mobilization of PBSC with minor side effects, which can markedly promote hematopoietic reconstitution after transplantation. The relative amount of CD3(+) lymphocytes significantly decreased and the ratio of CD4(+)/CD8(+) remained unchanged, which may lead to alleviation of a GVHD after PBSCT.