Objective To explore the relationship between the changes in cellular immunity and the causes of unexplained habitual abortion(UHA)as well as the mechanism of active immunotherapy on UHA patients.Methods T-lymphocyte and natural killer(NK)cell subsets(CD3+%,CD4+%,CD8+%,CD16+CD56+% and CD4+/CD8+ ratio)of peripheral blood were detected by applying flow cytometry and compared in 66 cases of UHA(UHA group,including 30 cases receiving active immunotherapy and 36 untreated UHA cases)and 30 cases of healthy fertile women(healthy control group).The re-pregnancy achievement ratio was compared between 30 treated UHA cases and 36 untreated UHA cases.Results The percentages of CD31+ and CD16+ CD56+ cells as well as CD4+/CD8+ ratio were significantly higher in UHA group than those of healthy control group(P＜0.050).As compared with those of untreated UHA subgroup,the percentages of CD3+ and CD16+ CD56+ cells as well as CD4+/CD8+ ratio were significantly lower(P＜0.050),while the re-pregnancy achievement ratio was higher(92.86% vs 05 29.03%,P＜0.001).Conclusion The changes in T-lymphocyte and NK cell subsets have something to do with occurrence of UHA.Active immunotherapy can regulate the cellular immune function and improve the re-pregnancy achievement ratio effectively.