β-Amyloid peptide (Aβ), a normal constituent of neuronal and non-neuronal cells, has been proven to be the major component of extracellular plaque of Alzheimer's disease. Interactions between Aβand neuronal membranes have been postulated to play an important role in the neuropathology of Alzheimer’s disease. Here we show that Aβ is able to insert into lipid bilayer. The membrane insertion ability of Aβ is critically controlled by the ratio of cholesterol to phospholipids. In a low concentration of cholesterol Aβ prefers to stay in membrane surface region mainly in aβ-sheet structure. In contrast, as the ratio of cholesterol to phospholipids rises above 30mol%, Aβ can insert spontaneously into lipid bilayer by its C terminus. During membrane insertion Aβ generates about 60%β-helix and removes almost all β-sheet structure. Fibril formation experiments show that such membrane insertion can reduce fibril formation. Our findings reveal a possible pathway by which Aβ prevents itself from aggregation and fibril formation by membrane insertion.