A.beta..sub.N3pE-42 is a .beta. amyloid protein that accumulates specifically as a major constituent of senile plaque in the brains of both sporadic and familial Alzheimer's disease patients. The invention provides antibodies that specifically recognize A.beta..sub.N3pE-42 and can be expected to have a strong .beta. amyloid-removing action. Particularly, humanized antibodies against A.beta..sub.N3pE-42 are useful to treat human neurodegenerative diseases. Further, since A.beta..sub.N3pE-42 is localized in the brain, the antibodies of the invention can avoid side effects such as kidney disorders caused by the formation of antigen-antibody complex in the blood. An agent for gene therapy using a vector in which a cDNA encoding a protein comprises the antigen-binding region of the antibody can be an efficient therapeutic drug for removing .beta. amyloid from the brain.