Aim To determine the platelet surface expression of glycoprotein Ⅱb/Ⅲa fibrinogen receptor （PAC-1） and P-selectin （CD62P） in diabetes mellitus （DM） patients with acute coronary syndrome （ACS） and to explore the relationship between them and plasma homocysteine （Hcy） level. Methods The platelet surface expression of PAC-1 and CD62P were measured by flow cytometry in 94 patients, including 40 ACS patients, 24 DM with ACS patients and 30 patients in control group. The correlation between platelet PAC-1, CD62P and plasma level of Hcy were investigated.