Previous studies have reported a neuroprotective effect of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) against traumatic brain injury. In accordance with the Marmarou method, rat models of diffuse axonal injury were established. 8-OH-DPAT was intraperitoneally injected into model rats. 8-OH-DPAT treated rats maintained at constant temperature served as normal temperature controls. TUNEL results revealed that neural cell swelling, brain tissue necrosis and cell apoptosis occurred around the injured tissue. Moreover, the number of Bax-, Bcl-2- and caspase-3-positive cells increased at 6 hours after diffuse axonal injury, and peaked at 24 hours. However, brain injury was attenuated, the number of apoptotic cells reduced, Bax and caspase-3 expression decreased, and Bcl-2 expression increased at 6, 12, 24, 72 and 168 hours after diffuse axonal injury in normal temperature control and in 8-OH-DPAT-intervention rats. The difference was most significant at 24 hours. All indices in 8-OH-DPAT-intervention rats were better than those in the constant temperature group. These results suggest that 8-OH-DPAT inhibits Bax and caspase-3 expression, increases Bcl-2 expression, and reduces neural cell apoptosis, resulting in neuroprotection against diffuse axonal injury. This effect is associated with a decrease in brain temperature. RESEARCH HIGHLIGHTS: (1) This study observed the neuroprotective effects of 8-hydroxy-2-(di-n-propylamino)tetralin against diffuse axonal injury, and explored its mechanism of action with respect to apoptosis.(2) 8-hydroxy-2-(di-n-propylamino)tetralin reduced brain tissue injury in rats, suppressed caspase-3 and Bax protein expression, enhanced Bcl-2 protein expression and reduced neural cell apoptosis.(3) The neuroprotective effect of 8-hydroxy-2-(di-n-propylamino)tetralin was associated with mild hypothermia in rats with diffuse axonal injury.