PURPOSE: To obtain an aromatic polysulfone of improved hydrophilicity, by bonding a specified aromatic polysulfone with a hydrophilic compound having an active eliminatable group through an ether bond.

CONSTITUTION: To a solution formed by dissolving an aromatic polysulfone terminated with an active monohydroxyphenyl group and having repeating units of any one of formulas IWV in 2W200pts.wt., per pt.wt. aromatic polysulfone, organic solvent is added atmost 10 mol, per jol of the polysulfone, of an alkali (e.g., NaOH), and the mixture is agitated at 10W120°C for 30minW2 hr. To this solution is added at most 50mol, per mol of the polysulfone, of a hydrophilic compound having an active eliminatable group [e.g., 2-[2-(2- chloroehoxy)ethyoxy]ethanol} dropwise, and the mixture is reacted for 30minW3 hr to bond the terminals of the aromatic polysulfone with the hydrophilic compound through an either bond.