We measured and compared the levels of plasma soluble (s) Pselectin, 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 antioxidized 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 factorexpressing 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.