Objective?To investigate the expression of miRNA-155 and its target gene in endometrium of the patients with repeated implantation failure.Methods?The infertile patients who were treated by in vitro fertilization and embryo transfer（IVF-ET）or intracytoplasmic sperm injection（ICSI）in the Department of Reproductive Medicine of our hospital from May 2018 to December 2019 were selected.The 15 patients who gave birth after the first assisted pregnancy in our hospital due to male factors or fallopian tube factors served as control group.The patients who have been transplanted at least three times（fresh or thawed embryos，each time with at least one high-quality embryo，and more than or equal to 4 of the number of transplanted high-quality embryos）were regarded as repeated implantation failure（RIF）group.There were 15 cases in control group and 15 cases in RIF group.The expressions of miRNA-155 and MMP16 mRNA in endometrium were detected by qPCR.The downstream target gene of miR-155 was detected by bioinformatics technology.The target gene of miR-155 was verified by double luciferase experiment.The expression of MMP-16 in endometrium of the patients with repeated implantation failure was detected by Western blot.The relationship between miRNA-155 and MMP16 was determined by correlation analysis.Results?The level of miR-155 in RIF group was significantly higher than that in control group（P＜0.05）.The results of bioinformatics technique，double luciferase reporter gene detection and transfection experiment indicated that miR-155 inhibited the expression of MMP16 mRNA and protein by binding to MMP 16 3′UTR.The results of qRT-PCR showed that the expression level of MMP16 mRNA and protein in RIF group was down-regulated，and the expression level of MMP16 mRNA was negatively correlated with the expression level of miR-155（r=-0.967，P＜0.05）.Conclusion?The expression of MiR-155 in endometrium of the patients with repeated implantation failure may be up-regulated，which may affect endometrial receptivity by regulating MMP-16 gene.