Abstract： Objective To determine the immunophenotypes of peripheral nature killer (NK) cells in patients with recurrent spontaneous abortion (RSA). Methods Flow cytometry was used to determine the expressions of CD56dimCD16+, CD56brightD16+/-, CD69+ and HLA-DR+ NK cells in peripheral blood samples from 27 pregnant and 41 non-pregnant RSA patients, 32 normal pregnant and 25 non-pregnant women, and the expressions were compared among 4 groups. Results The percentage of total peripheral NK cells from pregnant and non-pregnant RSA women, normal pregnant and non-pregnant women was (88.69± 5.86)％, (79.25±9.31 )％, (79.24±10.09)％ and (75.49±11.96)％, respectively, for CD56dimCD16+ NK cells; (8.18 ± 5.54)％ , (12.20 ± 6.49)％ , (13.13 ± 8.65)％ and (11.53 ± 6.23)％ , respectively, for CD56brightCD16+/- NK cells; (3.42±2.13)％ , (2.36± 1.72)％, (2.68± 1.81)％ and (2.08± 1.73)％ ,respectively, for CD69+ NK cells; (15.26±9.32)％, (9.96±7.18)％, (10.57±8.05)％ and (9.64±6.12)％,respectively, for HLA-DR+ NK cells. Compared with non-pregnant RSA women, normal pregnant or non-pregnant women, pregnant RSA women showed significantly higher percentage of CD56dimCD16% CD69+ and HLA-DR+ NK cells (all P＜0.05). Compared with non-pregnant RSA and normal pregnant women, pregnant RSA women showed significantly lower percentage of CD56brightCD16+/- NK cells (both P＜0.05).Conclusions The increased expression of CD56dimCD16+, CD69+ and HLA-DR+ NK cells and decreased expression of CD56brightCD16+/- NK cells in peripheral blood of the RSA pregnant patients may play a role in the development and progression of RSA.