The low-density lipoprotein-cholesterol (LDL-C) level of a 60-year-old woman diagnosed with acute coronary syndrome (ACS) was 212 mg/dL. She was suspected of having familial hypercholesterolemia, therefore, administration of a proprotein convertase subtilisin-kexin type 9 (PCSK9) antibody in addition to atorvastatin plus ezetimibe was initiated, reducing her LDL-C level to 42 mg/dL. Nine months after initial ACS, the PCSK9 antibody was discontinued. Six months after the iturruption, she relapsed with ACS, and neoatherosclerosis progression was confirmed via intravascular ultrasound. Then, the PCSK9 antibody was reintroduced. Disruption of a PCSK9 may be associated with the progression and destabilization of neoatherosclerosis. <Learning objective: Administration of a proprotein convertase subtilisin-kexin type 9 (PCSK9) antibody in addition to statin decreases low-density lipoprotein-cholesterol level and is effective in suppressing cardiovascular events, the effect on neoatherosclerosis after coronary artery stent deployment is not clear. We experienced an interesting reccurent ACS case with familial hypercholesterolemia, and reported the possibility that PCSK9 antibody disruption might contribute to destabilization of neoatherosclerosis after coronary stenting utilizing intravascular ultrasound.>.