Abstract. In this study, we investigated the effects of administration of coumestrol during pregnancy on calcium (Ca) metabolism in post-delivery maternal and neonatal mice. From 6.5 to 16.5 days post coitus (dpc), pregnant females were administered daily doses of coumestrol (200 µg/kg body weight/day). One day after parturition, blood samples and the kidneys, liver, jejunum and duodenum were obtained from each of maternal mouse, and blood samples and the kidneys and liver were obtained from neonatal mice. Coumestrol did not have any significant effect on the Ca and inorganic phosphorus concentrations in the sera of the maternal and neonatal mice. No notable effects of coumestrol were observed in relation to Vitamin D receptor expression in the maternal and neonatal mice by immunohistochemical analysis. Coumestrol did not affect the Vitamin D receptor and epithelial calcium channel1 and 2 mRNA levels in any of the organs investigated. Enzyme histochemical analysis showed that coumestrol decreased intestinal alkaline phosphatase activity in the maternal jejunum and duodenum. In the duodenum, coumestrol decreased expression of intestinal alkaline phosphatase, c-fos and vascular endothelial growth factor at the mRNA level. However, we did not observe any significant effects of coumestrol on the expression of these genes. In conclusion, coumestrol decreased intestinal alkaline phosphatase activity in the small intestines of maternal mice at the level used in the present study, and the mechanisms underlying this effect are different for the jejunum and duodenum. Key words: Coumestrol, Delivery, Epithelial calcium channels, Intestinal alkaline phosphatase, Mouse, Vitamin D receptor (J. Reprod. Dev. 54: [35][36][37][38][39][40][41] 2008) xogenous endocrine disruptors (EDs) are chemicals that exist in our environment and disrupt normal endocrine systems. Phytoestrogens, candidates of EDs, are plant-derived compounds that have a similar chemical structure to endogenous estrogen and the potential to mimic estrogen activity [1]. These chemicals can compete with 17β-estradiol for binding to estrogen receptors (ERs), although their relative affinity to ERs and transcription activity are substantially less than those of endogenous estrogens. Phytoestrogens can act as both estrogen agonists and antagonists [2]. Legumes are rich sources of phytoestrogens, and our foods and forage crops also contain them. There are several health benefits from these compounds, and phytoestrogens may help to prevent carcinomas, including breast, prostate and colon cancer, heart diseases, osteoporosis and menopausal disorders [2]. Thus, it is expected that phytoestrogens can be used to improve the health of humans, to prevent sickness and for estrogen replacement therapy (ERT). However, in the mid-20 th century, sheep fed a diet of predominately subterranean clover suffered from a reproductive disorder that reduced their lambing rates and produced abnormalities in the reproductive organs, permanent infertility, prolapsed uterus and maternal dys...