a urea adsorbent and a method for its production are disclosed , the adsorbent comprising hollow microspheres each having an outer layer formed of a urea - permeable polymer and an inner layer formed of a polymer containing a polyoxyalkylene glycol derivative expressed by the following formula : --. sub . n -- o --. sub . m r wherein r stands for hydrogen or a methyl group and n is an integer of 2 - 5 and m is an integer of at least 3 . the adsorbent can selectively adsorb urea with a high adsorbing activity and does not interact with other substances than urea and , therefore , is useful as an artificial kidney . the adsorbent may be prepared by subjecting a w / o / w type emulsion to polymerization wherein a radical polymerizable polyoxyalkylene glycol derivative is dissolved in the inner aqueous phase of the emulsion and an oil - soluble radical polymerizable monomer is used as the outer oil phase .