Telomerase is reactivated in lung cancer cells, the most prevalent cancer worldwide, but not normal cells. Therefore, targeting it, preferably with natural compounds derive from medicinal plant such as curcumin, could have important effect on treatment of lung cancer. Curcumin, derived from Curcuma longa rhizome, has many anti-cancer activities. Therefore, the main objective of current work was to study inhibitory effect of C. longa total extract on telomerase in A549 lung cancer cell line as in vitro model of lung cancer. First, total extract of C. longa were prepared by n-hexane, methanol and dichloromethane. Then, cytotoxic effect of n-hexane phase was studied on A549 lung cancer cell line with 24, 48 and 72 h MTT assays. Finally, after determination of IC50, cells were treated with n-hexane extract and TRAP (Telomeric Repeat Amplification Protocol) assay was done to measure amount of relative telomerase inhibition by the extract. Data analysis showed that n-hexane extract of C. longa has dose-dependent cytotoxic effect on A549 lung cancer cell line with IC50 = 0.23 - 0.28 mg/ml and the extract inhibits telomerase activity with dose-dependent manner. In conclusion, n-hexane extract of C. longa has cytotoxic and telomerase-inhibitory effect on cell line A549 and could be exploited as potential source for developing novel drugs against lung cancer.