Objective: To explore the effects of hyperbaric oxygen (HBO) treatment on the neuronal apoptosis at an earlier stage and the expressions of Cytochrome C (Cyt C), Bcl-2 (B-cell lymphoma-2 family) and Bax (Bcl-2associated X protein) in rat brain tissues after traumatic brain injury (TBI).Methods: Forty adult rats were divided into two groups, i.e., Group A ( the rats with untreated TBI) and Group B ( rats with HBO treatment after TBI). Sections of brain tissues of these two groups were then detected at 3,6,12,24,72 hours after TBI by immunohistochemistry and electronmicroscope, respectively.Results: HBO treatment could up-regulate the expression of Bcl-2 within 72 hours, reduce the release of Cyt C from mitochondria, attenuate the formation of dimeric Bax and alleviate the mitochondrial edema within 24 hours after TBI.Conclusions: HBO treatment can alleviate neuronal apoptosis after TBI by reducing the release of Cyt C and the dimers of Bax and up-regulating the expression of Bcl-2.