During pregnancy from the first trimester to a few months after delivery, some of the women suffer from depression. Amygdala is one of the central regions which regulate emotion. We investigate the effects of hormonal change during pregnancy and postpartum on the neuronal morphology and the expression of estrogen receptor α in the amygdala. We used virgin female Wistar rats [gestational day 15 (G15), 20 (G20), 4 days after delivery (P4) and estrous] to perform the Rapid Golgi Stain and immunohistochemistry. 1) The rat brains were stained by using the Rapid Golgi Stain protocol and coronally sectioned at 150 µm. We selected pyramidal neurons in the amygdala. And the dendritic spines were counted along the first branch of the apical dendrite and spine density was determined by counting the number of the spines in 10 µm. 2) Rats were perfused with paraformaldehyde. The brains were removed and coronally sectioned at 30 µm. The sections were incubated with anti-ERα for 4 days at 4°, and treated with diaminobenzidine (DAB). We counted the number of ERα immunoreactive cells in the amygdala. At P4, the number of mushroom type spine density in the amygdala was decreased compared with G15, G20 and estrous (p<0.05). Accordingly, at P4 the number of ERα immunoreactive cells in the central amygdala was decreased compared with G15 and G20 (p<0.05). These results suggest that the perinatal dynamic changes of the estradiol concentrations may affect to the morphological changes in the amygdala through the response with ERα, resulting in emotional instability.