The purpose of this study was to determine preventive and protective effects of chronic orally administration with quetiapine (QUE) against anxiety-like behavior and cognitive impairments in rats exposed to the enhanced single prolonged stress (ESPS), an animal model that is used to study post-traumatic stress disorder (PTSD), and to detect changes in the expression of cortical phosphorylated p44/42 extracellular-regulated protein kinase (pERK1/2). Before or after exposure to ESPS paradigm, consisting of 2-h constraint, 20-min forced swimming, ether-induced loss of consciousness, and an electric foot shock, rats were given orally QUE (10 mg/kg daily) for 14 days. Animals were then tested in the open field (OF), elevated plus-maze (EPM), and Morris water maze (MWM). Brains were removed for immunohistochemical staining of pERK1/2. ESPS exposure resulted in pronounced anxiety-like behavior compared to unexposed animals. ESPS-exposed animals also displayed marked learning and spatial memory impairments. However, QUE treatment (both before and after ESPS exposure) significantly ameliorated anxiety-like behavior, learning and spatial memory impairments. ESPS also markedly reduced the expression of pERK1/2 in the prefrontal cortex, medial amygdala nucleus, and cingulate gyrus. Both before and after ESPS exposure QUE treatments significantly elevated the reduced pERK1/2 expression in the three brain regions. QUE has preventive and protective effects against stress-associated symptoms and the changes in pERK1/2 functions may be associated with the pathophysiology of traumatic stress and the therapeutic efficacy of anti-PTSD therapy.