Origanum onites L. belongs to the Lamiaceae family which is commonly used for symptomatic treatment of the diseases of the gastrointestinal, endocrine, and respiratory systems in Turkish ethnobotanical studies and public. In this study our aim was to investigate the physiological effects of O. onites essential oil (OE) on A549 human lung cancer, MIA PaCa human pancreas cancer and HUVEC human endothelial cell lines. Our findings showed that O. onites OE treatment at all concentrations (4.79-191.6 µg/mL, 24 h) can inhibit cell proliferation and induce apoptosis in A549 and MIA PaCa cell lines (P < 0.0001). Although ≤19.16 µg/mL OE treatment for 24 h did not inhibit cell proliferation in the HUVEC cell lines, higher concentrations of OE (≥38.32 µg/mL) significantly inhibited cell proliferation. Apoptotic cell counts were significantly (P < 0.0001) higher in all cell lines at both incubation times (