Alzheimer disease (AD) is the most common form of dementia in aged population; it is a neurodegenerative disorder with unknown etiology and pathogenesis. The major pathological findings of AD include senile plaques, neurofibrillay tangles, and apoptosis-related regional synaptic and neuronal degeneration. The brain senile plaques are mainly produced by β-amyloid, a peptide with neurotoxicity and vasculotoxicity. Due to the polygenic and heterogeneous characteristics of AD, Amyloid Cascaded Hypothesis is currently drawing increasingly more attention. This paper reviews the relation between Aβ and AD published recently.