The purpose of the present invention is to provide an antibody againstfibroblast growth factor 23. The antibody is obtained by immunizing an animalwith a polypeptide which comprises an amino acid sequence represented by SEQID NO: 1, or an amino acid sequence derived from the amino acid sequencerepresented by SEQ ID NO: 1 by deletion, substitution, or addition of 1 orseveralamino acids, and has fibroblast growth factor-23 activity and activity tocontrol phosphate metabolism or vitamin D metabolism, and is shown by thefollowing (a), (b), or (c):(a) an antibody, which recognizes an amino acid sequence between the 180th andthe 194th, or the 237th and the 251st amino acid residues represented by SEQIDNO: 1；(b) an antibody, which is produced by a hybridoma whose accession number isFERM BP-7838, FERM BP-7839, FERM BP-7840, or FERM BP-8268； or(c) an antibody, which is competitive with the antibody produced by thehybridoma whose accession number is FERM BP-7838, FERM BP-7839, FERMBP-7840, or FERM BP-8268 upon binding with the polypeptide comprising theamino acid sequence represented by SEQ ID NO: 1.
