We measured and compared the levels of plasma soluble (s) P-selectin, sCD40L, platelet-derived microparticles (PDMP), monocyte-derived microparticles (MDMP), and anti-oxidized LDL antibody, to obtain a better understanding of their potential contribution to vascular complications in acute coronary syndrome (ACS). The concentrations of sP-selectin, sCD40L, PDMP, and MDMP in ACS patients were significantly higher than those in normal controls and patients with stable angina. When levels of these markers were compared with differences in concentration of anti-oxidized LDL antibody, all markers were significantly higher in ACS patients with a high level of anti-oxidized LDL antibody. Next, a monocytic cell line (THP-1) was incubated with high shear stress-induced platelet aggregates and PDMP. After incubation,THP-1 cells generated tissue factor-expressing MDMPs. This finding was particularly significant in the presence of oxidized LDL. These findings suggest that elevated levels of MDMPs may be a sign of atherosclerotic development in ACS patients, particularly those who exhibit anti-oxidized LDL antibodies.