In this study, we aimed to investigate ozonized oil nanoemulsions (OZNEs) as a radiosensitizer within B16 melanoma and OV-90 ovarian cells under X-ray irradiation in vitro. Radiation sensitivity of OZNE treated B-16 melanoma cells and OV-90 ovarian cells were evaluated by performing cell cycle analysis, Reactive Oxygen Species (ROS) and gamma-H2AX assays by flow cytometry. OZNEs induced G0-1 phase arrest of B-16 melanoma cells for all radiation doses and G2/M arrest for 8 Gy and 15 Gy doses. OZNE treated B16 melanoma and OV-90 ovarian cells induced DNA damage via the increase in ROS production, as well as significant increase in the expression of gamma-H2AX under even low doses of radiation (2 Gy). Thus, OZNEs are suggested to help to optimize cancer RT as a radiosensitizer and further studies will significantly outperform recent advances in this field.(c) 2022 Elsevier Inc. All rights reserved.