The object of the present invention is to provide a therapeutic agent for hyperphosphatemia capable sufficiently decreasing a serum phosphorus concentration with a small dose, and particles therefor. The present invention provides a therapeutic agent for hyperphosphatemia, which comprises, as an active ingredient, a particle containing a crosslinked polymer having a substituent containing a NRA1RA2 structure or a salt thereof, wherein the particle has an average particle diameter of 20 to 150 μm and a swelling rate of 9 to 16 mL/g (wherein RA1 and RA2 each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aminoalkyl group having 1 to 20 carbon atoms or a salt thereof, or the like).
