Objective:To evaluate the quantity and function changes of dendritic cells ( DC) in peripheral blood of patients with repeated implantation failure ( RIF).Methods:30 patients with RIF and 15 normal controls were enrolled in this study,and the peripheral blood was collected during the mid-luteal phase.The percentage of DC subsets and the expression levels of functional molecules were assessed by flow cytometric analysis.Results:Compared with normal controls,the percentage of lin-HLA-DR+DC cells accounting for leukocytes in patients with RIF was not significantly different ( P>0.05).There were also no significant differences in the expression levels of co-stimulatory molecules ( CD80 and CD86) and immune tolerant molecules CD200 on DC cells surfaces between patients with RIF and normal controls ( all P>0.05).In addition,the percentage of CD11c+CD123-mDC accounting for DC cells was significantly increased in patients with RIF (P<0.05),however,the percentage of CD11c-CD123+pDC was similar (P>0.05). Conclusion:The percentage of mDC accounting for DC cells was significantly increased in patients with RIF, which may be one of factors affecting pregnancy outcomes.