OBJECTIVE: Our previous studies demonstrated both phytoestrogen alpha-zearalanol (alpha-ZAL) and estrogen is effective decrease Alzheimer's disease (AD)-like apoptotic neuron death, but alpha-ZAL showed significantly less side-effect on breast and endometrial tissue compared to estrogen, it suggested that alpha-ZAL can be used as a potential substitute for estrogen. However, the molecular mechanism by which alpha-ZAL prevents neuron damage remains unclear. Growing evidence suggests that endoplasmic reticulum (ER) stress plays an important role in the process of cell apoptosis in AD; in addition, our published data indicated that alpha-ZAL possessed the potential ability to stabilize ER function. We therefore hypothesized that ER-stress mechanism maybe involved in the antiapoptotic effect of alpha-ZAL in this study. METHODS: Primary rat hippocampal neurons have been cultured and subsequently followed exposed to beta-peptide fragment 25-35(A beta(25-35)) with or without alpha-ZAL pre-treatment, and then western blot and flow cytometry techniques has been used to evaluate the intracellular calcium balance, ER stress and apoptotic cell death. RESULTS: The results showed that A beta(25-35) treatment for 24h induced dramatic neuronal apoptosis, accompanied by an increase in calpain2 expression, a marker of intracellular calcium overload. On the other hand, ER stress sensitive hallmarks, glucose-regulated protein 78 (GRP78), double-stranded RNA-dependent protein kinase (PKR)-like ER-resident kinase (PERK) and C/EBP homologous protein-10 (CHOP10) expressions were up-regulated after A beta(25-35) administration. Importantly, alpha-ZAL pre-treatment effectively attenuated above changes. CONCLUSION: These results demonstrated that alpha-ZAL protects cells against AD-like apoptosis and the effects at least partially by attenuating severely ER stress.