Polymer-grafted ion exchange adsorbents were of great interest for the development of high-performance pro-tein chromatography in biopharmaceutical and related fields. In this work, protein retention was systematically investigated in ion exchange chromatography packed respectively with dextran-grafted cation exchange adsor-bents containing sulphopropyl (SP) ligand, SP Sepharose XL and Capto S, and non-grafted cation exchange adsor-bent, SP Sepharose FF, using five proteins. With an increase of buffer pHs, retention factors of proteins decreased among all the adsorbents, demonstrating the dominant role of electrostatic interaction for protein binding on cat-ion exchange adsorbents. The evidences further revealed that the scattered positive charges on the surface of pro-tein molecules, rather than net charge of protein molecule, determined protein retention on cation exchange adsorbent. Likely, counterions including NH4+, K+, Na+and Mg2+exhibited distinct influence on protein reten-tion. It was well ascribed to solvent-mediated indirect ion–macromolecule interactions and direct ion–macromolecule interactions. Compared with SP Sepharose FF, polymer structure in dextran-grafted cation ex-change adsorbents ultimately brought about different ligand distributions and smaller pore sizes, thereby regu-lating protein retention in cation exchange chromatography. By comparing the retention of myoglobin andβ-lactoglobulinB in SP Sepharose XL and Capto S, we reasonably speculated that the enhancement of non-electrostatic interaction caused by reducing the space arm length was a major reason for an increasing retention factor of myoglobin in Capto S. The results in this research help us understand adsorption mechanism of protein in polymer-grafted adsorbents and give scientific guidance for the development of chromatographic materials. ? 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.