The present invention relates to a phosphate adsorbent on the basis of maghemite or maghemite/magnetite comprising (i) an iron oxide core comprising a crystal structure of inverse spinel iron oxide, (ii) a coating selected from monomeric carbohydrates, in particular monosaccharides or disaccharides, alditols, or mixtures thereof, and/or (iii) a pharmaceutical excipient selected from polymeric carbohydrates, wherein the phosphate adsorbent has the form of nanoparticles with a particle size of the iron oxide core (i) of less than 20 nm. The present invention further relates to a method for the production of a phosphate adsorbent on the basis of maghemite or maghemite/magnetite, to pharmaceutical compositions comprising the phosphate adsorbent, and to medical uses thereof, especially for the prevention and/or treatment of hyperphosphatemia.