The present invention relates to a GCP II (glutamate carboxypeptidase II) mutant (K699S) having the activity of inhibiting glutamate production and the activity of cleavaging β-amyloid, and to a pharmaceutical composition for the prevention and treatment of a disease selected from the group consisting of amyloidosis, Alzheimer's disease, Down syndrome accompanying Alzheimer's disease, stroke, dementia, Huntington's disease, Pick's disease, and Creutzfeldt-Jakob disease comprising the GCP II mutant (K699S) as an active ingredient. The GCP II (glutamate carboxypeptidase II) mutant (K699S) demonstrates not only excellent Aβ cleavage activity compared with the wild type GCP II but also excellent activity of inhibiting glutamate production, unlike the wild type GCP II, so that the mutant has been confirmed to have higher effect and stability than the wild type, suggesting that the GCP II mutant can be effectively used for the prevention or treatment of neurodegenerative diseases.
