Abstract: Objective To explore the effect of stroma cell-derived factor receptor CXCR4 on the homing of the hematopoietic stem/progenitor cells in utero transplantation. Methods CD34+ cells were separated by Ficoll density gradient centrifugation and MiniMACS and stimulated for 48h by SCF、IL-6 cytokines prior to transplantation. The changes of the CD184(CXCR4) expressions and transmigrate rates of the CD34+ cells were analysed by flow cytometer. The 1 105 cells pretreated with different treatment were transplanted into the abdominal cavity of the fetal BALB/c mouse in the pregnant days 13~14. The human CD45 cells as the marker of graft were detected by flow cytometry after 1 month the fetus born. Results Expression changes of CD184 on CD34+ cells were from 9.58% 1.56％ to 19.32% 3.64％ after SCF and IL-6 stimulation. The CD34+/CXCR4high cells exhibited significant increases in SDF-1 mediated chemotaxis compared with the CD34+/CXCR4low cells. Transmigration of CD34+/CXCR4high was inhibited by pretreatment with antiCXCR4mAb and PTX. The positive rates of human CD45 cells detected in the fetal mouse were significantly higher in the SCF and IL-6 pretreatment group. This effects were significantly abrogated after the addition of antiCXCR4mAb or PTX. Conclusion Up-regulation of CXCR4 expression may be useful for improving hematopoietic stem/progenitor cells homing in utero transplantation. This homing process is mediated and depended on the CXCR4 receptors. The signal transduction is mediated by PTX-sensitive Gi protein.