Objective:To investigate the expression of Toll-like receptor 4(TLR4)and extracellular signal-regulated protein kinase 1/2(ERK1/2)in decidua tissue of patients with unexplained spontaneous abortion and their correlation.Methods:The expres-sions of TLR4,ERK1/2 and p-ERK1/2 in decidua tissues of 32 patients with unexplained spontaneous abortion(abortion group)and 32 normal pregnancy(control group)were detected by immunohistochemistry and Western blot,respectively.The correlation between TLR4 and p-ERK1/2 in abortion group were analyzed by Pearson hierarchical correlation analysis.Results:In immunohistochemical experiments,the cytoplasm of decidua cells in the two groups is the expression locus of TLR4,ERK1/2 and p-ERK1/2,the expression of the three proteins were different,and the expressions of TLR4 and p-ERK1/2 in abortion group were significantly higher than that in control group(P<0.01).There was no significant difference in ERK1/2 expression between abortion group and control group(P>0.05);In decidua tissue samples of abortion group,the protein level of TLR4 was higher than that of control group(P<0.05);the pro-tein level of p-ERK1/2 was significantly higher than that of control group(P<0.01),and the protein level of ERK1/2 in decidua tissue of abortion group was not statistically different from that of control group(P>0.05).TLR4 was positively correlated with p-ERK1/2 expression in abortion group(r=0.890,P<0.01).Conclusion:Abnormal activation of TLR4/ERK1/2 signaling pathway may be one of the mechanisms of unexplained spontaneous abortion.