The aim of this study was to explore the effects of the stromal cell-derived factor (SDF-1) and chemokine receptors (CXCR4) on chemotaxis of cord blood AC133(+) cells. The optimal SDF-1 concentration was determined in Transwell System. The cell migration was calculated from the number of cells passing through polycarbonate membrane with 8 microm pore. The expressions of CXCR4 in fresh and cultured cord blood AC133(+) cells were analyzed by flow cytometry with two-color direct immunofluorescence. The results showed that the chemotactic rate of fresh cord blood AC133(+) cells increased along with increasing concentrations of SDF-1, however, it tended to be stable when the concentration of SDF-1 reached 150 ng/ml. There was no difference in the chemotactic rate of cord blood AC133(+) cells between the group with SDF-1 adding CXCR4-blocking antibody and the group without SDF-1. When AC133(+) cells were cultured in vitro with hemopoietic growth factors, the expression of CXCR4 increased at the early stage, but decreased gradually along with time extending. In conclusion, there was correlation between the chemotactic rate of AC133(+) cells and the expression of chemokine receptor CXCR4.