Recurrent spontaneous abortion (RSA) is reported to be associated with immune imbalance at the maternal-fetal interface. Immune cells in the decidual tissue are involved in maintaining immune tolerance during pregnancy; however, whether natural killer (NK) and T cells are altered in unexplained RSA (URSA) remains unknown. In this study, we compared the number and percentage of CD56(+) NK cells, CD4(+) T cells and CD8(+) T cells by flow cytometry in 30 URSA patients and 30 normal pregnant controls. We found that there are a higher proportion of CD4(+) T cells and CD16(+)CD56(+) NK cells and a lower number of CD8(+) T cells in the decidual tissue of URSA patients compared to normal controls. In addition, the number of T helper type 1 (Th1) cells and the Th1/Th2 ratio were higher in URSA patients compared to normal pregnant controls. In conclusion, our results indicate that the changes in the proportion of local T lymphocyte subsets, NK and Th1 cells, in the maternal-fetal interface may be related to occurrence of URSA.