Aromatic hyperbranched polymers, such as hyperbranched poly(ether sulfone), are promising catalytic materials, but the advantages of the hyperbranched structure have not been well understood. In this study, hyperbranched poly(ether sulfone), functionalized with sulfonic acid terminal groups (HBSPES) and its linear analogue (LSPES), were studied as acid catalysts for a model reaction, namely, the esterification of 1-butanol and acetic acid. In the homogeneous catalytic reaction, HBSPES showed a clear advantage in the apparent turnover frequency (TOF). To utilize these polymers as heterogeneous catalysts, they were immobilized onto carbon black (CB) to obtain HBSPES/CB and LSPES/CB. The polymer loading after immobilization was higher with HBSPES/CB, probably due to the dense architecture of the hyperbranched polymer. In the heterogeneous catalytic reaction, HBSPES/CB exhibited a much better catalytic performance than LSPES/CB, possibly benefiting from the good affinity of the hyperbranched polymer to the reaction solution. These experimental observations suggest that aromatic hyperbranched polymers are suitable for use as catalysts. (C) 2018 Elsevier Ltd. All rights reserved.