Objective: To explore the expression of serum levels of platelet activating factor (PAF) and its correlation to the property of coronary plaque in patients with different types of coronary artery disease (CAD). Methods: A total of 138 patients received coronary angiography (CAG) in our hospital from 2013-01 to 2013-12 were studied. According to CAG and clinical presentation, the patients were divided into 3 groups: Control group, the subjects with normal coronary artery, n=33, ACS (acute coronary syndrome) group, n=65 and SAP (stable angina pectoris) group, n=40. Serum levels of PAF were detected by ELISA, coronary lesions were examined by intravascular ultrasound (IVUS), and the correlation between PAF levels and plaque properties were studied. Results: ① Compared with Control group, ACS group and SAP group had increased serum levels of PAF; PAF level in ACS group was even higher than SAP group, both P<0.05. ② IVUS examination indicated that there were 30/40 (75.0%) patients with hard plaque in SAP group and 44/67 (67.7%) patients with soft plaque in ACS group. Compared with SAP group, ACS group were mainly having eccentric plaques and increased rates of plaque rupture (24.6% vs 7.50%), thrombus formation (21.5% vs 0%), plaque positive remodeling (46.1% vs 25.0%) and eccentric index (0.70 ± 0.22) vs (0.30 ± 0.24), all P<0.01;the external elastic membrane area was similar between SAP group and ACS group, P>0.05. ③ PAF levels were similar in fibrous, calcified and mixed plaques, P>0.05; while they lower than that in soft plaque, P<0.05. Conclusion: ① Serum PAF was involved in coronary plaque formation, unstable plaque usually had the higher PAF level.② PAF level may provide a new reference for ACS diagnosis, treatment and prognosis.