The objective of this study was to investigate the expression of steroid hormone receptors in human first trimester placenta and decidua and whether such expression was altered after mifepristone treatment. One hundred women who requested termination of pregnancy between 7 and 12 wk were randomly assigned to receive placebo or 200 mg mifepristone at 12, 24, and 48 h before suction evacuation of uterus. Immunohistochemistry was used to detect the expression of progesterone receptor, estrogen receptor, glucocorticoid receptor (GR), and androgen receptor. Progesterone receptor expression in both placenta and decidua tissues was not affected by mifepristone treatment. Estrogen receptor was identified in a decidual gland in only one sample. Androgen receptor was not expressed in either tissue. The expression of GR in decidual stromal cells was suppressed by mifepristone, and the effect was detectable at 12 h after administration. The expression of GR in decidual glands was not affected. In the placenta, the expression of GR in cytotrophoblasts and villous stromal cells was suppressed by mifepristone; the effect was detectable at 12 h and persisted at 48 h. In conclusion, the suppressed GR expression after mifepristone administration may be part of the mechanism of mifepristone in causing abortion.