Atractylon was extracted from Atractylodes. Determination of atractylon in Atractylodes rhizome was achieved with only a few mg of crude drug sample. Addition of atractylon also attenuated the genotoxicity of t-BHP evaluated by unscheduled DNA synthesis. The sum of the results suggested that the protective effect of atractylon against oxidative stress induced by t-BHP is via its ability to quench superfluous free radicals.