Postpartum depression (PPD) has adverse effects on offspring and increases their vulnerability to psychiatric disorders such as depression. Akt-mTOR signaling in the hippocampus is implicated in depression but its role in the behavioral deficits in PPD offspring remains unknown. By using a prepregnancy stress model of PPD in which Balb/c females that experience chronic stress before pregnancy show long-lasting PPD-like behaviors, we tested depression-like behaviors in PPD offspring (PPD-F1) at juvenile and adult ages as well as in the second generation (PPD-F2) produced by cross of male PPD-F1 with naïve females. Hippocampal Akt-mTOR signaling was examined in the F1 and F2 generations of PPD, as well as in PPD-F1 mice treated with a single dose of the antidepressant ketamine. PPD-F1 showed depression-like behaviors at juvenile and adult stages, evidenced by reduced sucrose preference (SP), increased immobility time in the forced swim test (FST), and a longer latency to feed and reduced food consumption in the novelty suppressed feeding (NSF) test. PPD-F1 mice showed Akt-mTOR signaling deficiency in the hippocampus, with down-regulated expression of p-Akt, p-mTOR and p-p70S6K. A single dose of ketamine reversed the behavior deficits and the impairment in Akt-mTOR signaling in PPD-F1. Furthermore, the PPD-F2 mice remained deficient in the SP and NSF test and hippocampal Akt-mTOR signaling, although the performance in FST was normal. The present study demonstrated both long-term and transgenerational effects of PPD on the depression–like behaviors of offspring, and suggested impaired Akt-mTOR signaling may play a part.