Abstract: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by β-amyloid (Aβ) deposition as an important pathological feature. Anti-Aβ monoclonal antibodies have provided a new modality for disease-modifying therapy, and Aβ PET/CT imaging is of great clinical significance in the early diagnosis, therapeutic efficacy assessment, and dynamic monitoring of disease status in AD. The author reports a patient with AD treated with an anti Aβ monoclonal antibody, in whom ¹⁸F-flobetapir (AV45) PET/CT imaging was used to evaluate therapeutic efficacy by comparing the imaging changes in cerebral Aβ before and after lecanemab treatment, in combination with semiquantitative analysis parameters standardized uptake value ratio (SUVR) and Centiloid (CL) values and clinical cognitive function-related scales such as the Alzheimer's disease assessment scale-cognitive subscale (ADAS-cog) and the clinical dementia rating. In this case, post-treatment ¹⁸F-AV45 PET/CT directly showed a marked reduction in Aβ deposition in patient′s brain tissue (decreased SUVR and CL values), whereas among contemporaneous clinical cognitive function-related scores, only ADAS-cog improved, providing a noninvasive examination method for clinical efficacy evaluation and disease monitoring. Moreover, through a literature review, this case report further deepens the understanding of the application value of Aβ PET/CT in the diagnosis and treatment of AD.