Cerium oxide (ceria) contains two stable states of cerium ions (Ce3+and Ce4+). The presence of these two states and the ability to swap from one state to another (Ce3+Ce4+) by scavenging the highly reactive oxygen species (ROS) generated from radiolysis of water, ensure the enhanced stability of polysulfone (Psf) membranes in the γ-radiation environment. In this study, the ROS scavenging ability of ceria was studied. Ceria nanoparticles were found to scavenge ROS like hydroxyl radicals and hydrogen peroxide (H2O2). The H2O2scavenging is due to the peroxidase-like catalytic activity of ceria nanoparticles. The ROS scavenging is responsible for offering protection to the Psf host matrix and in turn the stability to the Psf-ceria mixed-matrix membranes( MMMs) in γ-radiation environment. Thus, presence of ceria nanoparticles provides an opportunity for utilizing PsfceriaMMMsin ionizing radiation environment with increased life span, without compromise in the performance. © 2021 De Gruyter. All rights reserved.