Objective: To investigate the changes in proportion and function of the CD4 T cells and regulatory cells (CD4+CD25highCD127– Treg cells) in peripheral blood of arteriosclerosis (AS) patients. Methods: AS patients (AS group) and healthy subjects undergoing health maintenance examination (healthy control group) were selected with 40 cases in each group, and then the samples of peripheral venous blood were obtained. Using flow cytometry, the proportions of CD4 T cells, CD8 T cells, IFN-γ+ CD4 T cells, TNF-α+ CD4 T cells and CD4+CD25highCD127– Treg cells were measured, and the changes in ability of proliferation and cytokine secretion of the CD4 T cells after co-culture with respective CD4+CD25highCD127– Treg cells were also determined. Results: In AS group compared with healthy control group, the proportion of CD4 T cells and CD4 T/CD8 T ratio were significantly increased and the proportions of IFN-γ+ CD4 T cells and IFN-α+ CD4 T cells were also significantly increased (all P<0.05), but the proportions of CD8 T cells and CD4+CD25highCD127– Treg cells showed no significant difference (both P>0.05). In healthy control group, the abilities of proliferation and IFN-γ and IFN-α secretion in CD4 T cells were all significantly lower in co-culture with CD4+CD25highCD127– Treg cells than those in single culture (all P<0.05), while these parameters in AS group showed no significant difference between single culture and co-culture (all P>0.05). Conclusion: There is loss of function of CD4+CD25highCD127– Treg cells in AS patients, which results in the increased proportion and cytokine secretion ability of CD4 T cells, and thereby triggers the inflammatory state in AS.