The rhomboid nucleus of the bed nucleus of the stria terminalis (BSTrh) is one of the important brain regions for infanticide. We previously revealed that excitatory synaptic transmission in the BSTrh is potentiated in adult male mice compared with those before sexual maturation. However, it remains unclear how sexual hormone mediates this behavioral transition and plastic changes in the neural circuit underlying behavioral selection for pups during sexual maturation. Here, we found that continuous administration of estradiol (E2) to gonadectomized mice during sexual maturation elicited infanticidal behaviors in adulthood (about 7 weeks old). Next, we performed whole-cell patch clamp recording in the BSTrh to study the effect of altered gonadal steroid hormones levels on neural synaptic transmission. We found that E2 administration considerably enhanced excitatory synaptic transmission in the BSTrh by increasing the probability of glutamate release from the presynaptic terminals. These data suggest that reinforcement of excitatory synaptic transmission by estrogen-receptor-dependent signaling in the BSTrh during sexual maturation may contribute to the expression of infanticidal behaviors. We currently explore the source of excitatory synaptic inputs into the BSTrh.