Objective:To explore effects of carnosine on peripheral blood T-lymphocyte immunity in MCAO rats and the neuroprotective mechanisms. Methods: Thirty-six male SD rats were randomly divided into three groups: the sham-operated group (n=12), the model group (n=12), and the carnosine-treated group (n=12). The middle cerebral artery occlusion model was established by suture method in the model group and the carnosine-treated group. After establishment of MCAO model, the rats in the carnosine-treated group were lavaged with soluble canosine once a day at the dose of 1 000 mg/kg, and the same volume of normal saline was lavaged in the sham operation and model group. The neurological function was scored with Longa 5-point scale at baseline, 24 h and 72 h. The level of peripheral blood T-lymphocyte subset (CD3+, CD4+, CD8+) was detected by flow cytometry at 24 and 72 h, and calculate CD3+/CD8+ ratio. The infarction volume was revealed by TTC stain at 72 h. Results: The infarction volumn was detected in both of the model group and the camosine-treated group. Compared with the model group, the infarction volume was smaller (P < 0.05); Compared with the model group, there was no significant different in the neurological outcome scores in the carnosine-treated group at baseline and 24 h (P > 0.05); however, there was a significant decrease at 72 h of the carnosine-treated group (P < 0.05); Compared with the sham-operated group, the level of CD3+, CD4+ and the CD4+/CD8+ ratio was significant decreased (P < 0.05) and the level of CD8+ was increased in the model group at 24 and 72 h (P < 0.05). Compared with the model group, the level of CD8+ was significant decreased in the carnosine-treated group at 72 h (P < 0.05). Conclusions: Carnosine could has potential protective effective on peripheral immune suppression of MCAO rats and the mechanism could be CD3+, CD4+/CD8+ elevation and CD8+ inhibition.