Chitosan-catechin conjugate was prepared to examine cellular radical scavenging activity in mouse macrophage cells. No cytotoxicity was observed in the tested concentrations (50~400 μg/mL) of chitosan-catechin conjugate. Chitosan-catechin conjugate inhibited intracellular reactive oxygen species (ROS) formation determined by a fluorescence probe, 2,7-dichlorofluorescin diacetate (DCFH-DA), and the inhibition activity was 32.82% at 200 μg/mL, whereas unmodified chitosan showed 26.29% at the same concentration, indicating ROS scavenging activity was increased by conjugating catechin onto chitosan. Chitosan-catechin conjugate also inhibited lipid peroxidation by 1.07-fold compared with the control (non-treatment group). Furthermore, chitosancatechin conjugate up-regulated the expression of cellular glutathione level by 2.07-fold compared with non-treatment group.