Plant-derived bioactive compounds attract considerable interest as potential chemopreventive anticancer agents. We analyzed the volatile dietary phytochemicals (terpenes) present in mastic oil extracted from the resin of Pistacia lentiscus var. chia and comparatively investigated their effects on colon carcinoma proliferation, a) in vitro against colon cancer cell lines and b) in vivo on tumor growth in mice following oral administration. Mastic oil inhibited -more effectively than its major constituentsproliferation of colon cancer cells in vitro, attenuated migration and downregulated transcriptional expression of survivin (BIRC5a). When administered orally, mastic oil inhibited the growth of colon carcinoma tumors in mice. A reduced expression of Ki-67 and survivin in tumor tissues accompanied the observed effects. Notably, only mastic oil -which is comprised of 67.7% α-pinene and 18.8% myrceneinduced a statistically significant anti-tumor effect in mice but not α-pinene, myrcene or a combination thereof. Thus, mastic oil, as a combination of terpenes, exerts growth inhibitory effects against colon carcinoma, suggesting a nutraceutical potential in the fight against colon cancer. To our knowledge, this is the first report showing that orally administered mastic oil induces tumor-suppressing effects against experimental colon cancer.Plant-derived bioactive compounds attract nowadays considerable interest as potential chemopreventive anticancer agents. Chemoprevention refers to the strategy of using bioactive natural or synthetic compounds to inhibit cancer progress 1 . Naturally occurring compounds in plants, phytochemicals, have been under thorough investigation for the identification of potent anti-cancer agents with great success and, thus, are considered the backbone of pharmaceutical innovation 2 . Dietary phytochemicals which derive from edible plants such as vegetables, fruits and herbs, form a distinct and very promising class of chemopreventive nutraceuticals. In particular, certain bioactive dietary phytochemicals (e.g. curcumin) have been shown to contribute to colon cancer prevention or therapy 3, 4 .The incidence of colorectal cancer is now increasing in countries where it was previously low, such as certain Asian (e.g. Japan) and Eastern European (e.g. Czech Republic) countries 5 , indicating the influence of westernized lifestyle and specifically unhealthy diet on the prevalence of colon cancer risk. It has been estimated that a substantial proportion (approximately 35%) of new cancer cases in Western countries, can be prevented only by dietary means 6 , suggesting that dietary modifications or nutritional interventions may be beneficial for colorectal cancer prevention.Essential oils from aromatic plants have been shown to possess diverse biological activities 7 and are a great source of dietary phytochemicals, being mixtures of biologically highly active compounds 8 . One of the main classes of chemical compositions found in essential oils are isoprenic derivatives, that include monoterpenes