This study was carried out to investigate the protective effects of chitosan nanoparticles (CNP) against hydrogen peroxide (H₂O₂)-induced oxidative damage in murine macrophages RAW264.7 cells. After 24 h pre-incubation with CNP (25-200 μg/mL) and chitosan (CS) (50-200 μg/mL, as controls), the viability loss in RAW264.7 cells induced by H2O2 (500 μM) for 12 h was markedly restored in a concentration-dependent manner as measured by MTT assay (P < 0.05) and decreased in cellular LDH release (P < 0.05). Moreover, CNP also exerted preventive effects on suppressing the production of lipid peroxidation such as malondialdehyde (MDA) (P < 0.05), restoring activities of endogenous antioxidant including superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) (P < 0.05), along with increasing total antioxidant capacity (T-AOC) (P < 0.05). In addition, pre-incubation of CNP with RAW264.7 cells for 24 h resulted in the increase of the gene expression level of endogenous antioxidant enzymes, such as MnSOD and GSH-Px (P < 0.05). At the same concentration, CNP significantly decreased LDH release and MDA (P < 0.05) as well as increased MnSOD, GSH-Px, and T-AOC activities (P < 0.05) as compared to CS. Taken together, our findings suggest that CNP can more effectively protect RAW264.7 cells against oxidative stress by H₂O₂ as compared to CS, which might be used as a potential natural compound-based antioxidant in the functional food and pharmaceutical industries.