Aims: To investigate whether patients with acute coronary syndrome (ACS) possessed high levels of platelet-monocyte aggregates (PMAs) and related circulating biomarkers.Methods: 74 ACS patients, 58 stable angina pectoris (SAP) patients and 46 control patients without coronary artery disease were selected and their PMAs were measured by flow cytometry. Their plasma IL-6, IL-8, MCP-1, soluble CD40L and soluble P-selectin were also measured simultaneously by flow cytometry. Results: Patients with ACS exhibited higher level of PMAs compared with SAP patients and the control. Furthermore, the levels of IL-6, IL-8, MCP-1, soluble CD40L, soluble P-selectin and CRP were also significantly higher in ACS patients than in SAP patients and the control group. However, there were no significant difference in the levels of IL-8, sCD40L, sP-selectin and CRP between SAP patients and the control group. Correlation analysis showed that high levels of IL-6 and sP-selectin were significantly correlated with PMAs. Logistic analysis further demonstrated that the presence of elevated CRP, IL-6 and PMAs level each confers an increased risk of ACS. Conclusion: Elevated levels of PMAs and related circulating biomarkers might indicate the unstable coronary syndrome in ACS patients, and the levels of PMAs, CRP and IL-6 could be used for monitoring and guiding the early intervention of ACS patients.