Abstract: Objective To explore the clinical value of PET-CT for the diagnosis of unstable plaques in atherosclerotic lesions. Methods 60 cases underwent whole-body ¹⁸F-FDG PET-CT were retrospectively evaluated, including 6 cases with normal control group and 54 cases with atherosclerotic plaques. 54 cases with SUV and CT value in atherosclerotic lesions of large arterial wall were detected retrospectively. 54 high ¹⁸F-FDG uptake cases in atherosclerotic plaques were divided into three groups according the CT value:soft plaques group, intermediate plaques group, calcified plaques group. Group 4 was normal. Results In soft plaques group there were 42 sites whose average SUV was 1.553±0.486, in intermediate plaques group there were 30 sites whose average SUV was 1.393±0.296, in calcified plaques group there were 36 sites whose average SUV was 1.354±0.189, in normal control there were 33 sites whose average SUV was 1.102±0.141. The SUV showed significant difference among the four groups (F=678.909, P=0.000). There were significant difference between normal ¹⁸F-FDG uptake group and high ¹⁸F-FDG uptake groups. Conclusions ¹⁸F-FDG had different degree high uptake in large atherosclerotic plaques, the soft plaques had the highest ¹⁸F-FDG uptake among them. The results suggested that ¹⁸F-FDG PET-CT had significant potential valuable in the diagnosis of unstable soft plaques in atherosclerotic lesions.