Patients 65 years and older account for an increasing proportion of traumatic brain injury (TBI) patients. Aged TBI patients experience increased morbidity and mortality compared with young TBI patients. We previously demonstrated a marked accumulation of CD8 + T-cells within the brains of aged TBI mice compared with young TBI mice. Therefore, we hypothesized that blocking peripheral T-cell infiltration into the injured brain would improve neurocognitive outcomes in aged mice after TBI. Young and aged male C57BL/6 mice underwent TBI via controlled cortical impact versus sham injury. Two hours after injuries, mice received an anti-CD49d antibody (aCD49d Ab) to block peripheral lymphocyte infiltration or its isotype control. Dosing was repeated every 2 weeks. Mortality was tracked. Neurocognitive testing for anxiety, associative learning, and memory was assessed. Motor function was evaluated. Plasma was collected for cytokine analysis. Flow cytometry was used to phenotype different immune cells within the brains. Consequently, aCD49d Ab treatment significantly improved post-TBI survival, anxiety level, associative learning, memory, and motor function in aged mice 2 months after TBI compared with isotype control treated mice. aCD49d Ab treatment augmented T H 2 response in the plasma of aged mice 2 months after TBI compared with isotype control-treated mice. Notably, aCD49d Ab treatment significantly reduced activated CD8 + cytotoxic T-cells within aged mouse brains after TBI. Contrastingly, no difference was detected in young mice after aCD49d Ab treatment. Collectively, aCD49 Ab treatment reduced T-cells in the injured brain, improved survival, and attenuated neurocognitive and gait deficits. Hence, aCD49d Ab may be a promising therapeutic intervention in aged TBI subjects-a population often excluded in TBI clinical trials.