One of the most common cancers that result in death is lung cancer. There is new hope in the ght against lung cancer thanks to the chemopreventive properties of natural dietary substances like β- caryophyllene oxide (CPO), and research is currently being done to test this theory. CPO, a sesquiterpene isolated from medicinal plant essential oils, inhibits carcinogenesis and has been effective in treating many cancers. This study examined how CPO affected proliferation of human lung cancer A549 cells. CPO was found to have an inhibitory concentration (IC50) of 124.1 g/ml.