Abstract： Objective To evaluate the "Instant Method" in enzyme-linked immunosorbent assay (ELISA)by detecting matrix metalloproteinase-9 (MMP-9) and to discuss the quality control in the serum in patients with coronary artery disease (CAD). Methods The level of MMP-9 in the serum of patients with CAD was measured by MMP-9 ELISA Kit, and "Instant Method" was used for internal quality control. Results MMP-9 levels were measured in MMP-9 ELISA Kit and the coefficient of variance (CV) was no higher than 15%. The value of SI between 0.625 and 1.15 was in the acceptable range. The level of MMP-9 significantly increased in the serum of the patients with myocardial infarction compared with the health control and angina pectoris. Conclusion "Instant Method" is an effective approach for internal quality control.