Post-traumatic stress disorder (PTSD) is a trauma- and stressor-related disorder, characterized by bi-directional symptomatic manifestations of increase in both hyperarousal/hypervigilance and numbing/avoidance. In our previous reports, we have proposed an animal model of PTSD using avoidance/escape task sessions in the shuttle box after delivering an inescapable foot-shock traumatization in the same box (Wakizono et al., 2007), and demonstrated the efficacy of 2-week administration of antidepressant on the hyperarousal/hypervigilant behavioral parameters (Sawamura et al., 2004) in the model. In this study, we observed a partial but significant efficacy of oral supplementation of eicosapentaenoic acid (EPA) for five weeks on the numbing/avoidance behavior in the experimental model. Additionally, western blot analyses using brain-derived neurotrophic factor (BDNF) monoclonal antibody revealed a decreased expression of BDNF protein, in the hippocampal region of the rats, due to foot-shock traumatization and a significantly increased expression of BDNF protein after oral EPA supplementation. The results indicate a possibility that alteration of the numbing/avoidance behavior parallels the expression of hippocampal BDNF in the rat brain. The present study suggests a possibility that EPA supplementation in the treatment of PTSD ameliorates persistent numbing/avoidance symptoms. (185 words).