The aim of the present study was to examine the protective effect of γ-mangostin, a component of the mangosteen shell, against oxidative damage to nerve cells induced by excessive glutamate, a known excitatory neurotransmitter. To investigate the effect of γ-mangostin on apoptosis, 5 mM of glutamate was used to induce apoptotic cell death in mouse hippocampal HT22 cells. In this study, γ-mangostin was found to exert a stronger protection than N-acetyl cysteine against glutamate-induced cell damage. γ-Mangostin showed prevented glutamate-induced apoptosis in HT22 cells by reducing the production of reactive oxygen species and stimulating the expression of heme oxygenase-1 protein. In addition, glutamate significantly induced the accumulation of intracellular calcium ions, whereas treatment with γ-mangostin markedly reduced it. Hoechst 33342 staining showed an improvement in glutamate-induced nuclear condensation following γ-mangostin treatment. Furthermore, the number of annexin V-positive cells was significantly reduced following treatment with γ-mangostin. Western blot analysis showed the inhibition of glutamate-induced mitogen-activated protein kinase phosphorylation by γ-mangostin. γ-mangostin also inhibited the regulation of the intrinsic mitochondrial apoptotic pathway. Thus, the results of this study suggest that γ-mangostin is an active ingredient of mangosteen and exerts neuroprotective activities in HT22 cells.