The present invention is directed to a phosphate ion adsorbent comprising a polymer or a salt thereof with a metal complex group represented by the following general formula (II): bound thereto directly or through a spacer. The phosphate ion adsorbent of the present invention is advantageous not only in that the adsorbent specifically adsorbs phosphate ions in a living body, but also in that the adsorbent has high adsorbability to phosphate ions, thus useful in removing the phosphate ions from the living body.