Epidemiological studies have suggested that long-term use of nonsteroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX) activity can moderate the onset or progression of Alzheimer's disease (AD). Thus it has been suggested that prostaglandin E2 (PGE2), a major end-product of COX, may play a pathogenic role in AD, but the involvement of PGE synthase (PGES), a terminal enzyme downstream from COX, has not been fully elucidated. Here we found that, among three PGES enzymes, only microsomal PGES-1 (mPGES-1) is induced, and its expression is associated with β-amyloid (Aβ) plaques in the cerebral cortex in human AD patients and in Tg2576 mice, a transgenic AD mouse model. Furthermore, to investigate whether mPGES-1 contributes to AD-like pathology, we bred mPGES-1-deficient mice with Tg2576 mice. We found that mPGES-1 deletion reduced the accumulation of microglia around senile plaques and attenuated learning impairments in Tg2576 mice. These results indicated that mPGES-1 is induced in the AD brain and thus plays a role in AD pathology. Blockage of mPGES-1 could form the basis for a novel therapeutic strategy for patients with AD. Inc. © 2013 Wiley Periodicals, Inc.