Chitosan, as a novel bioadditive antioxidant for commodity polymer, is proposed. Chitosan is successfully conjugated with deoxycholic acid and gallic acid (chitosan-DC-GA) via a simple reaction using the 1-ethyl-3-(3'-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide conjugating agent at room temperature in a heterogeneous system. Chitosan-DC-GA shows a deoxycholic acid (DC) and gallic acid (GA) content of about 40% each. Chitosan-DC-GA exhibits DPPH radical scavenging ability with EC50 1 mg mL(-1) based on the EPR technique evaluation. A model case study of chitosan-DC-GA with low-density polyethylene (LDPE) confirms improvement in compatibility, as seen from the sheet clarity, as well as the good dispersion of chitosan-DC-GA in LDPE matrices, as observed by scanning electron microscope. (C) 2008 Wiley Periodicals, Inc.