A fundamental feature of Alzheimer disease (AD) is the accumulation of beta-amyloid (Abeta), a peptide generated from the amyloid precursor protein (APP). Emerging evidence suggests that soluble Abeta oligomers adversely affect synaptic function, which leads to cognitive failure associated with AD. The Abeta-induced synaptic dysfunction has been attributed to the synaptic removal of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs); however, it is unclear how Abeta induces the loss of AMPARs at the synapses. In this study we have examined the potential involvement of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), a signaling molecule critical for AMPAR trafficking and function. We found that the synaptic pool of CaMKII was significantly decreased in cortical neurons from APP transgenic mice, and the density of CaMKII clusters at synapses was significantly reduced by Abeta oligomer treatment. In parallel, the surface expression of GluR1 subunit as well as AMPAR-mediated synaptic response and ionic current was selectively decreased in APP transgenic mice and Abeta-treated cultures. Moreover, the reducing effect of Abeta on AMPAR current density was mimicked and occluded by knockdown of CaMKII and blocked by overexpression of CaMKII. These results suggest that the Abeta-induced change in CaMKII subcellular distribution may underlie the removal of AMPARs from synaptic membrane by Abeta.