Telomerase is active in more than %85 of cancers including lung cancer but not in the normal cells. In addition, lung cancer is the most prevalent cancer worldwide. Therefore, targeting the telomerase in this cancer could be promising step in its treatment. Different agents have been proposed for telomerase inhibition. But, they have undesirable effects and it is necessary to study alternative telomerase-inhibiting agents, preferably natural compounds. Curcuma longa is a medicinal plant which its constituents, especially curcumin, has diverse anti-cancer properties including anti- telomerase action. Anti-telomerase action of pure curcumin has been studied previously. However, to date any study for investigating the effect of curcuma total extract on telomerase remains unperformed. Therefore, the main aim of current thesis was to study the effect of curcuma longa total extract on telomerase inhibition in A549 cells as in vitro model of lung cancer.