Glutamate is the major excitatory neurotransmitter in the central nervous system and plays a critical role in maintaining normal neuronal function. However, excessive extracellular accumulation of glutamate under pathological conditions induces excitotoxicity, which is closely associated with oxidative stress, mitochondrial dysfunction, and subsequent neuronal cell death. S-allyl cysteine (SAC) is a compound derived from aged garlic, known for its antioxidant and potential cardioprotective properties. The present study investigated the neuroprotective effects of SAC against glutamate-induced cytotoxicity in mouse hippocampal HT22 cells. HT22 cells were exposed to glutamate to establish an in vitro oxidative neurotoxicity model. SAC was administered 2 h prior to glutamate exposure to evaluate its protective potential. Cell viability was assessed using the MTT assay, and glutamate-induced morphological changes were examined by phase-contrast microscopy. Glutamate treatment significantly reduced cell viability in a dose-dependent manner and induced characteristic neuronal damage, including cell shrinkage, dendritic loss, and decreased cell density. SAC treatment alone did not affect cell viability, indicating that SAC is non-cytotoxic within the tested concentration range. Notably, pretreatment with SAC significantly attenuated glutamate-induced cytotoxicity and improved glutamate-induced morphological alterations, thereby preserving neuronal structure and reducing cellular damage. In conclusion, SAC exerts significant protective effects against glutamate-induced oxidative neurotoxicity in HT22 cells. These findings suggest that SAC may serve as a promising neuroprotective agent for excitotoxicity-related neurological disorders.