AIM: To explore the effects of interferon-α (IFN-α) application on peripheral circulating CD1α dendritic cells (DCs)in patients with chronic hepatitis B, and the expression of HLA-DR, CD80, and ICAM-1 on CD1α DCs in order to explore the mechanism of immune modulation of IFN-α.METHODS: By flow cytometry technique, changes of CD1α DCs were monitored in 22 patients with chronic hepatitis B treated with IFN-α and in 16 such patients not treated with IFN-α within three months. Meanwhile,the expression of HLA-DR, CD80, and ICAM-1 on CD1αDCs was detected.RESULTS: In the group of IFN-α treatment, the percentage of CD1α DCs in peripheral blood mononuclear cells was increased after three months of therapy. In patients who became negative for HBVDNA after IFN-α treatment, the increase of DCs was more prominent, while in control, these changes were not observed. Increased expression of HLA-DR,CD80, and ICAM-1 on CD1α DCs was also observed.CONCLUSION: CD1α DCs can be induced by IFN-α in vivo, and the immune related molecules such as HLADR, CD80, and ICAM-1 are up-regulated to some degree.This might be an important immune related mechanism of IFN-α treatment for chronic hepatitis B.