Apolipoprotein D (Apo D) is a lipid binding protein whose expression is strongly induced in the mammalian brain during aging and age-dependent neurodegenerative diseases such as Alzheimer's disease (AD), where it can play an important function as a neuroprotective and antioxidant protein. Increasing evidence suggests that the gradual increase in free radicals and oxidative stress with age is the primary determinant to aging brain. The aim of this work is to study the effect of hydrogen peroxide (H2O2) in Apo D expression, in hippocampal cells, in order to investigate the relationship between oxidative stress and elevated levels of Apo D found in hippocampus during aging and AD and also elucidate the possible pathways that lead to this increase. In this study, we demonstrated that Apo D expression in hippocampal neurons of aged and AD brains directly correlates with age-related increase in oxidative stress. More importantly, our results in the HT22 cell line indicate that Apo D protein level increases in a concentration-dependent manner specifically at those H2O2 concentrations that caused oxidative damage and apoptotic cell death. These data support the idea that oxidative stress-induced apoptosis during aging and AD may be associated with the increment in the expression of Apo D in these situations.