Objective: This work aimed to elucidate the natural killer cells role during embryonic implantation process and its possible relation in abortion. Methods: A bibliographical revision was made based on scientific articles from electronic databases as Google academic, Scielo and PUBMED, and books, published in Portuguese and English, from 2003 to 2019. Results: During female reproductive cycle, NK cells act in ovulation and allows the discernment of changing from endometrium in decomposition (menstruation) to decidualization in pregnancy. In addition, NK may also influence implantation and presents a correlation with recurrent abortion. Conclusion: NK's performance in female deciduous is still controversial, so it is necessary more studies to better understand this subject.

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