摘要：Objective:To determine the activity and phenotype of decidual natural killer (NK) cells in patients with unexplained habitual abortions (UHA).Methods:A total of 32 patients with UHA were studied, and 20 cases of normal pregnant women were selected as control group. The levels of CD56+CD3- NK cells and their CD56+CD16-, CD56+CD16+ subsets in decidua were detected using two-color flow cytometric analysis.The NK cells activity was measured by a chromium-51(51Cr) release cytotoxicity assay,with K562 human myeloid leukaemia cells as targets.Results:Compared with control group, the proportion of CD56+CD3- NK cells in decidual mononuclear cells(DMC) of UHA patients had no difference, but the CD56+CD16- NK cell subset decreased and the CD56+CD16+ subset increased significantly (P＜0.05). The decidual NK cells activities of UHA patients were higher than those of normal controls (P＜0.05).Conclusions:NK cell is predominant lymphocyte in normal decidua and plays an important role in maintaining successful pregnancy. Abnormally raised activity and disbalanced CD56+CD16+, CD56+CD16- subsets of decidual NK cell are associated with UHA and may play a role in reproductive failure.