Abstract Disulfonated poly(arylene ether sulfone)s are high glass transition temperature polymers, and their water and salt transport properties depend sensitively on thermal processing history. In this study, films of a 32 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-32), polymerized in the potassium counter-ion form, were acidified using solid state and solution routes. The resulting acid counter-ion form materials were then converted to sodium, potassium, and calcium counter-ion forms via ion exchange. Additionally, several films were subjected to various thermal treatments in the solid state. Water uptake as well as water and NaCl permeability of these BPS-32 films were measured. Acidification via immersion of BPS-32 films in boiling sulfuric acid solution increased water uptake, and water and salt permeability increased. Exposure of samples to elevated temperature also influenced transport properties. For example, immersing BPS-32 films in boiling water for 4 h increased water sorption by 50%, water permeability by 2.3 times, and NaCl permeability by 8 times. The counter-ion form of the sulfonated polymer influenced the polymer’s transport properties, but these effects were weaker than the effect of thermal treatment. Generally, the BPS-32 samples prepared with different processing histories followed a trade-off between water/salt permeability selectivity and water permeability. These results suggest that, like many other glassy polymers, thermal processing history influences small molecule transport in these materials.