Alzheimer's disease (AD) is the most common form of dementia in the elderly. It is generally believed that β-amyloidogenesis, tau-hyperphosphorylation, and synaptic loss underlie cognitive decline in AD. Rps23rg1, a functional retroposed mouse gene, has been shown to reduce Alzheimer's β-amyloid (Aβ) production and tau phosphorylation. In this study, we have identified its human homolog, and demonstrated that RPS23RG1 regulates synaptic plasticity, thus counteracting Aβ oligomer (oAβ)-induced cognitive deficits in mice. The level of RPS23RG1 mRNA is significantly lower in the brains of AD compared to non-AD patients, suggesting its potential role in the pathogenesis of the disease. Similar to its mouse counterpart, human RPS23RG1 interacts with adenylate cyclase, activating PKA/CREB, and inhibiting GSK-3. Furthermore, we show that human RPS23RG1 promotes synaptic plasticity and offsets oAβ-induced synaptic loss in a PKA-dependent manner in cultured primary neurons. Overexpression of Rps23rg1 in transgenic mice consistently prevented oAβ-induced PKA inactivation, synaptic deficits, suppression of long-term potentiation, and cognitive impairment as compared to wild type littermates. Our study demonstrates that RPS23RG1 may reduce the occurrence of key elements of AD pathology and enhance synaptic functions to counteract oAβ-induced synaptic and cognitive deficits in AD.