Abstract: Objective: To observe the changes of CD3⁺CD8⁺CD28^- suppress T lymphocytes(Ts) and CD3⁺CD8⁺CD28⁺ cytotoxic T lymphocytes(Tc) subsets in peripheral blood of SD rats with spinal cord injury(SCI).Methods: The SCI model of ten female SD rats were established using New York University Spinal Cord Contusion system.The changes of CD3⁺CD8⁺CD28^- and CD3⁺CD8⁺CD28⁺ T cell subsets in peripheral blood were evaluated using flow cytometry at the time points of pre-injury and days 1,3,5,7,14,21,28 and 56 post-injury.Results: The percentages of Ts and Tc in the CD3⁺ T cells of peripheral blood of healthy rats were(30.27±12.09)% and(14.75±4.29)%,respectively.The percentage of Ts was(22.58±12.12)% at the first day of SCI.At the 5th day,it decreased to the lowest level(20.86±10.41)%,it reached to the normal level from 7 to 21d after SCI.At 28th day,it increased to(37.90±12.98)%.At 56th day(33.79±11.44)%,it decreased to the normal level again(P>0.05).The change trend of Tc was opposite to the Ts after SCI.The percentages of Tc at time points of days 1,5,21 and 28 post-injury were(17.29±7.10)%,(20.02±6.24)%,(23.89±6.78)% and(13.81±11.21)%,respectively.It didn't return to normal level,but decreased to(8.71±6.44)% at the time points of 56 d(P<0.01).Conclusions: In the early stage of SCI,Tc are predominant in the peripheral blood of SD rats,which suggest that the function inhibition of Ts and enhancement of Tc may be one of the important immune injury mechanism of the SCI.The period from 5 to 21 days post-injury may be a key time window for the immunomodulatory treatment of SCI.