Aim To study the relationship between peripheral blood CD4⁺CD25⁺regulatory T cell（Treg） and carotid atherosclerosis in patients with cerebral infarction. Methods The study included 56 patients with cerebral infarction and with carotid plaques confirmed by high resolution MRI, and included the same period healthy patients （control group） with 30 cases as research subjects. Patients were classified according to the characteristic findings of plaques in MRI. Levels of peripheral blood CD4⁺CD25⁺Treg was determined by flow cytometry. Results The percentage of peripheral blood CD4⁺CD25⁺Treg in infarction patients was lower than the control group（P<0.05）. The percentage of peripheral blood CD4⁺CD25⁺Treg in patients of unstable plaques group, unrupture plaques group and rupture plaques group were significantly lower compared with individuals of stable plaques group （P<0.05，P<0.01）. The percentage of peripheral blood CD4⁺CD25⁺Treg in patients of rupture plaques group was significantly lower compared with individuals of unrupture plaques group（P<0.05）. The percentage of peripheral blood CD4⁺CD25⁺Treg was negatively correlated with the stability of carotid plaques. Conclusions There was a relationship between peripheral blood CD4⁺CD25⁺Treg and carotid atherosclerosis. Low serum levels of the markers may indicate that the plaques were vulnerable or ruptured.