Adolescent stress can be a risk factor for abnormal social behavior in the postpartum period, which critically affects the safety of mothers and children. Nonetheless, the underlying mechanisms remain unclear. Using a newly established mouse model with optogenetics and in vivo calcium imaging, we found that adolescent psychosocial stress, combined with pregnancy and delivery, caused hypofunction of the glutamatergic pathway from the anterior insula to prelimbic cortex (AI-PrL pathway), which altered PrL neuronal activity, and in turn led to abnormal social behavior. Specifically, the AI-PrL pathway played a crucial role during recognizing the novelty of other mice by modulating ″stable neurons″ in PrL, which were constantly activated or inhibited by novel mice. We also observed that glucocorticoid receptor signaling in the AI-PrL pathway had a causal role in stress-induced postpartum changes. Our findings provide novel and functional insights into a cortico-cortical pathway underlying adolescent stress-induced postpartum social behavioral deficits.