Abstract: The present disclosure relates to a composition for preventing or treating lung cancer, comprising a compound isolated from a Cephalotaxus extract as an active ingredient. Isoharringtonine, which is the compound isolated from the Cephalotaxus extract according to the present disclosure, induces apoptosis and exhibits the effect of inhibiting the growth of non-small cell lung cancer cell lines, and thus can be useful in the prevention or treatment of lung cancer. In addition, the combined treatment of isoharringtonine and siNR4A1 enhances anticancer activity, and the combined treatment of isoharringtonine and cisplatin, which is a conventional anticancer drug, induces a high anticancer effect at a low concentration of cisplatin, thereby reducing side effects of anticancer treatment.