In previous studies, researchers observed that doxepin could improve cognitive processes and has protective effects on the central nervous system. Thus, this study was designed to analyze the effects of doxepin on β-amyloid (Aβ)-induced memory impairment and neuronal toxicity in rat and to explore the underlying mechanism.Rats were treated with Aβ1-42 and doxepin was injected to validate its effects on cognitive function. The Morris water maze test was performed to detect memory function. Aβ1-42-treated SH-SY5Y human neuroblastoma cell line was also used to detect the effects of doxepin and to explore the underlying mechanism. Western blotting analysis was used to detect the protein expression levels of PSD-95, synapsin 1, p-AKT and p-mTOR in rats.After treated with 1 mg/kg of doxepin, Aβ1-42-treated rats showed markedly lower escape latency and higher platform-finding strategy score. Low doses of doxepin significantly reversed the effects of Aβ1-42 on the protein expression levels of PSD-95, synapsin 1, p-AKT and p-mTOR in rats. In vitro experiment showed the consistent results. Besides, PI3K inhibitor (LY294002) treatment could markedly reversed the effects of doxepin on Aβ1-42-treated SH-SY5Y cells.Our results demonstrated that doxepin could protect against the Aβ1-42-induced memory impairment in rats. The protective effect of doxepin was associated with the enhancement of PSD-95 and synapsin 1 expression via PI3K/AKT/mTOR signaling pathway.