To provide a protein having acetylcholine esterase (AChE) activity derived from a plant and a gene encoding the protein and to provide a method for refining the protein and a method for measuring the AChE activity.

A protein having acetylcholine esterase activity derived from the plant and composed of (a) a specific amino sequence or (b) an amino acid sequence in which a part of amino acids is lost, substituted or added in the specific amino sequence, the gene encoding the protein, the method for refining the protein from a plant body, a protein obtained by the such method and the method for measuring the acetylcholine activity by using neostigmine.