A polyarylene copolymer which comprises (A) from 60 to 3 mol % aromatic compound units having a main chain containing one or more electron-withdrawing groups therein and (B) from 40 to 97 mol % aromatic compound units having a main chain containing no electron-withdrawing groups therein (provided that (A)+(B)=100 mol %), and a proton-conductive membrane comprising the polyarylene copolymer having sulfonic acid groups.