Aim To investigate the effects of oxidized LDL （ox-LDL） on peripheral blood level of regulatory T cells （Tregs） in patients with acute coronary syndrome （ACS）. Methods 18 patients with acute myocardial infarction （AMI）, 27 patients with unstable angina （UA）, 23 patients with stable angina （SA） and 30 healthy subjects （NC） were recruited. The plasma levels of ox-LDL and IL-10 were measured by ELISA, and the percentage of Tregs in peripheral blood were detected by flow cytometry. Peripheral blood mononuclear cells （PBMC） were prepared by Ficoll density gradient, then were incubated with ox-LDL for 48 h for analysis of flow cytometry. Results The frequencies of Tregs and level of IL-10 were significant lower in AMI and UA patients than those in the SA and NC groups, while the level of ox-LDL was elevated markedly in patients with AMI and UA compared with SA and NC group. In addition, the levels of plasma ox-LDL were negatively correlated with the levels of Tregs and IL-10. Moreover, the peripheral blood level of Tregs was obviously decreased after incubation with ox-LDL for 48 h. Conclusion ox-LDL could down-regulate the peripheral blood level of Tregs in patients with ACS, thereby promoting the progression of ACS.