PURPOSE: To offer an adsorbent with improved biological compatibility, a selective adsorbability and a deterioration resistance, by using a specified substance as a polymer for coating the adsorbent.

CONSTITUTION: In an adsorbent having a surface coated with a polymer, the coating polymer is a substance containing one or more of crosslinked hydrophilic polymers (except a hydroxylalkyl methacrylate polymer). The polymer includes a lot of hydrophilic radicals, e.g. OH radicals, COOH radicals, etc., bonded to a polymer chain. The polymer may be crosslinked after a substrate adsorbent such as active carbon is coated with an uncrosslinked polymer, or may be precrosslinked before dissolved and then applied onto the substrate adsorbent. The crosslinking may be done in various manners. But, an aqueous solution or suspension of a water-insoluble polymer shall be used in the coating method. A polymer, but not a monomer, shall be used in the treatment of the substrate adsorbent, i.e., a water-soluble or water-dispersible polymer shall be used.