Estrogen has been shown to contribute greatly to growth and development in endometrial cancer. And recent research has suggested that intratumoral production of estrogen may play important roles in this cancer tissue. On the other hand, pregnane X receptor (PXR), a new member of nuclear receptors, has been shown to mediate the genomic effects of steroid hormones, including estrogen and xenobiotics. And this receptor is thought to regulate the expression of the cytochrome P-450 3A (CYP3A) gene family, which plays important roles in the metabolism of endogenous steroids and xenobiotics. Various levels of PXR expression were found in endometrial cancer tissues but not normal tissues. Tissues showing high PXR expression showed significantly high expression of CYP3A4/7 and low expression of estrogen receptor (ER) compared with levels in tissues showing low PXR expression. In endometrial cancer cell lines, HEC-1 cells, which express high PXR and low ER and progesterone receptor, show a stronger transcriptional response of the PXR-CYP3A pathway to the PXR ligands, especially endocrine-disrupting chemical, than do Ishikawa cells. These data suggest that the steroid/xenobiotics metabolism in the tumor tissue through PXR-CYP3A pathway might play an important role, especially in alternative pathway for gonadal hormone and endocrine-disrupting chemical effects on endometrial cancer expressing low ER alpha.