Abstract: AIM:To analyze the relationship between the osteoprotegerin (OPG) system and stabilization of coronary artery atherosclerosis in patients with acute coronary syndrome (ACS). METHODS: A total of 575 consecutive patients were divided into three groups: ACS group (n=335), stable angina (SA) group (n=120) and control group (n=120). ACS group was subdivided into unstable angina (UA) group of 134 patients, non-ST-segment elevation myocardial infarction (NSTMI) group of 80 patients and ST-segment elevation myocardial infarction (STMI) group of 121 patients. Serum OPG and its ligand (souble-RANKL, sRANKL) levels were measured by enzyme-linked immunosorbent assay (ELISA). The relationship between levels of OPG and sRANKL as well as the ratio of the two (OPG/sRANKL) and stabilization of coronary artery atherosclerosis was investigated. RESULTS: Serum OPG, sRANKL, and OPG/sRANKL ratios were different between ACS, SA and control groups (P<0.01). Serum OPG, sRANKL and OPG/sRANKL ratios were different among the three subgroups of ACS group (P<0.05). The difference between STMI group and UA group was significant (P<0.05). The difference between UA group and NSTMI group and the difference between NSTMI group and STMI group were not significant. Gensini coronary points were positively correlated with both serum OPG levels (r=0.252, P<0.01) and OPG/sRANKL (r=-0.284, P<0.01), but negatively correlated with serum sRANKL levels (r=-0.235, P<0.05). CONCLUSION: OPG and sRANKL levels and the ratio of the two (OPG/sRANKL) are associated with the stabilization of coronary artery atherosclerosis in patients with ACS.