Substantial amount of caryophyllene oxide (CPO) is present in the essential oils of traditionally-used folk medicinal plants and herbal spices. The CPO, produced via chemical and/or enzymatic reaction of caryophyllene (CP), has largely being used as a flavoring component and exhibited a variety of biological activities. Now, we report the antimutagenic activity of CPO determined by Ames`s preincubation test. S-9 fraction was prepared from the liver of rats treated with Arochor 1254. Aflatoxin B₁ (AFB₁) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) were used as mutagens. Reduction of mutagenicity of AFB₁ or IQ for S. typhmurium TA98 and TA100 by CPO was found to be a dose-dependant manner. CPO (500 ㎍/plate) reduced mutagenicity of AFB1 for S. typhimurium TA98 and TA100 to 89% and 71%, respectively. For IQ, similar results were observed against S. typhimurium TA98 and TA100, resulting in the inhibition percentage of 77% and 51%, respectively. CP also reduced mutagenicity of AFB₁ and IQ far S. typhimurium TA98 and TA100, but the reduction rate was somewhat lowered relative to that of CPO. These results indicate that CPO could be developed as a potent antimutagenic flavoring agent.