CD4+ T cells mainly interact with Sphingosine 1-phosphate (S1P) to regulate immune function through Sphingosine 1-phosphate receptor 1 (S1P1). This study was aimed to investigate the effects of recombinant human granulocyte-colony-stimulating factor (rhG-CSF) mobilization on S1P1 expression in CD4+ T cells of donor's peripheral blood. The CD4+T cells of peripheral blood were isolated by magnetic beads from 17 allo-hematopoietic stem cell transplantation (allo-HSCT) donors before and at fourth day of mobilization with rhG-CSF. The S1P1 expression was detected by real time quantitative PCR in the RNA extracted from CD4+ T cells collected before and after rhG-CSF mobilization. The results showed that the expression of S1P1 was found in CD4+ cells before and after rhG-CSF mobilization, but the expression level of SIP1 in CD4+ cells after rhG-CSF mobilization was significantly lower than that before rhG-CSF mobilization (p<0.01). It is concluded that the mobilization with rhG-CSF obviously down-regulates the expression of S1P1 in CD4+ T cells of donor's peripheral blood.