A phosphorus adsorbent, which is used for adsorbing phosphorus in extracorporeal circulation, is a powder comprising a carbonate of a rare earth metal or an oxide of a Group 4 element and having a solubility in 100 g of water at 20° C. of 10 mg or less. The porous fiber, which comprises the phosphorus adsorbent carried therein, shows a change in pH value of from −1.0 to +1.0 inclusive before and after stirring in physiological saline for 4 hours. The phosphorus adsorption columns respectively comprise the phosphorus adsorbent and the porous fiber each disposed therein.
