Abstract: Objective: To observe changes of the level of soluble plasma CD40 ligand (sCD40L) and matrix metalloproteinase-9 (MMP-9) in patients with various coronary heart diseases and their correlations with the development of acute coronary syndrome (ACS), and to evaluate the significance of sCD40L and MMP-9 as plasma target of plague rupture. Methods: Forty-eight patients with ACS, 17 with stable coronary heart disease (SCHD) and 15 normal controls were concluded in the study. Their plasma levels of sCD40L and MMP-9 were measured with enzyme-linked immunosorbent assay. Results: The plasma level of sCD40L in patients with ACS was significantly higher than that of patients with SCHD and normal controls (P<0.01). MMP-9 level was significantly higher in patients with ACS than in those with SCHD and normal controls (P<0.01). There was a positive correlation between the levels of sCD40L and MMP-9 (P<0.01). Conclusions: The plasma levels of both sCD40L and MMP-9 are elevated significantly in patients with acute coronary syndrome, which suggests that they may have close correlation with the rupture of the unstable atheromatous plagues and may serve as a potential marker of plague stability.