Interferon-induced transmembrane protein-3 (IFITM3) belongs to the IFITM family, which comprises five and seven subtypes in humans and mice, respectively. IFITM proteins participate in various biological processes such as the immune response, including suppression of viral infection. While the immune response is associated with the pathology and development of Alzheimer’s disease (AD), it is unknown whether this response is beneficial or harmful. Recently, IFITM3 was found to be a γ-secretase modulatory protein, a type of protein associated with the generation of amyloid b (Aβ). However, further research is needed to determine whether IFITM3 is associated with abnormal behaviors, including cognitive impairment in AD, and whether it may be a new molecular target for AD therapy. Since our final goal is to clarify the role of IFITM3 in an animal model of AD, in this study we used App-KI mice, which overproduce Aβ-42 without overexpressing amyloid precursor protein, to examine changes in IFITM3 expression. The cortex, dentate gyrus (DG), and CA3 regions of 4- and 8-month-old App-KI mice exhibited Aβ accumulation and also increased IFITM3 expression. Expressions of astrocytes and microglia were age-dependently increased around Aβ plaques. Notably, IFITM3 expression colocalized with astrocytes, which were situated near Aβ in all brain regions of 8-month-old App-KI mice. These results suggest that IFITM3 is increased in astrocytes and is accompanied by Aβ accumulation.