Abdominal aortic aneurysm (AAA) is a common disease among the elderly. Recently, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors have been indicated as useful therapeutic tools for the treatment of cardiovascular diseases. The aim of this study was to elucidate the role of PCSK9 in the pathogenesis of AAA. We used fluorescence immunohistochemistry to assess the expression of PCSK9 in aortic tissues resected from 24 patients with AAA. Histological examination showed that PCSK9 expression in the adventitia region of the aneurysms was decreased in AAA samples. In the same region, the expression of CD36 increased. We hypothesized that CD36 expression might upregulate the transport of fatty acids into cells such as the adipocytes, and subsequently cause degradation of the adventitia in the aortic wall, contributing to AAA development.