Disclosed is an aromatic sulfonic acid ester derivative represented by the formula (1); ##STR00001## in the formula, X is an atom or a group selected from a halogen atom excluding fluorine, --OSO.sub.3CH.sub.3 and --OSO.sub.3CF.sub.3, A is a divalent electron attractive group, B is a divalent electron donating group or a direct bonding, R.sup.a is a hydrocarbon group of 1 to 20 carbon atoms, Ar is an aromatic group having a substituent of --SO.sub.3R.sup.b (wherein R.sup.b is a hydrocarbon group of 1 to 20 carbon atoms), m is an integer of 0 to 10, n is an integer of 0 to 10 and k is an integer of 1 to 4. Also disclosed is a process for producing a polyarylene having a sulfonic acid group, which process comprises the steps of coupling polymerization of an aromatic compound containing the derivative of the formula (1), to prepare a polyarylene and hydrolysis of the polyarylene, and which process has high safety and is easily capable of controlling the amount of sulfonoc acid group introduced into a polymer and the introducing position thereof.