Estrogen affects a variety of brain functions, including higher functions. The estrogen level is persistently high during pregnancy and then declines rapidly with delivery, which causes the brain to be subjected to marked effects during this period. Thus, pregnant and parturient women are prone to altered mental activity and have a higher probability of anxiety and depressive disorders, which may be caused by marked changes in estrogen levels. The central nucleus (CeA) and basolateral nucleus (BLA) of the amygdala and the anterior division (BNSTa) and principal nucleus (BNSTp) of the bed nucleus of the stria terminalis are regions involved in emotional processing, including anxiety, and also target brain areas of estrogenic action. However, the expression of estrogen receptors during this period is not clear. In this study, we analyzed the distribution of estrogen receptor α (ERα)-immunoreactive cells at gestational days 7 (G7) (early gestation), 14 (G14) (mid-gestation), 21 (G21) (late gestation), and 4 days after delivery (P4) (early postpartum) in rats. In the CeA, the number of nuclear ERα-positive cells decreased significantly at G7, G14, and G21. In the BLA, distribution of ERα was detected in the cell body (indicating membrane-associated ERα) with a trend toward decreased immunoreactivity during pregnancy. The BNSTp showed no changes, but in the BNSTa, nuclear ERα-positive cells were significantly reduced at G14, G21, and P4. These regional differences in changes of ERα-positive cells may be involved in the symptoms of anxiety and depression during pregnancy and the postpartum period.