A medical adsorbent for oral administration that has low dosage and excellent adsorptive capacity and selective adsorption for toxins to be removed, and is also economical and environmentally friendly. The medical adsorbent comprises granular activated carbon that is activated carbon obtained by carbonization and activation of refined cellulose or regenerated cellulose, and having a mean pore diameter of 1.5 to 2.2 nm, a BET specific surface area of 700 to 3000 m2/g, a mean particle size of 100 to 1100 μm, a surface oxide content of 0.05 meq/g or greater and a packing density of 0.4 to 0.8 g/mL, and it can be used as a therapeutic or prophylactic agent for kidney disease or liver disease, for oral administration.