Abstract: Objective To study the correlation between the expression of B lymphocyte activating factor in decidual and chorionic membranes and early spontaneous abortion.Methods Thirty women with early spontaneous abortion served as an experimental group and 30 women who had artificial abortion for normal early pregnancy served as a control group.Expression of B lymphocyte activating factor in decidual and chorionic membranes was detected by immunohistochemistry.Results B lymphocyte activating factor was expressed in all samples of decidual and chorionic membranes.However,its expression level in decidual membrane was lower in experimental group than in control group（P＜0.05）.B lymphocyte activating factor was not expressed in angioendothelium of experimental group.Conclusion B lymphocyte activating factor is associated with early spontaneous abortion and may be one of the reasons for early spontaneous abortion.