Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 4 2023 08 27 565 573 Fatemeh Rasti Student Research Committee, Fasa University of Medical Sciences, Fasa, Iran Elahe Ahmadi Medicinal Plants Research Center, Fasa University of Medical Sciences, Fasa, Iran Mojdeh Safari Department of Medical Nanotechnology, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran Abbas Abdollahi Department of Microbiology, School of Medicine, Fasa University of Medical Sciences, Fasa, Iran Saha Satvati Department of Medical Biotechnology, School of Advanced Technologies in Medicine, Fasa University of Medical Sciences, Fasa, Iran Razie Ranjbar Noncommunicable Disease Research Center, Fasa University of Medical Sciences, Fasa, Iran Mahmoud Osanloo Department of Medical Nanotechnology, School of Advanced Technologies in Medicine, Fasa University of Medical Sciences, Fasa, Iran 2023 06 02 2023 08 10 Background and Objectives: This study aimed to develop a natural nanoemulsion with antibacterial and anticancer properties. Materials and Methods: The chemical composition of the Origanum majorana essential oil was investigated using GC–MS analysis. Besides, the successful loading of the essential oil in the nanoemulsion was confirmed using ATR-FTIR analysis. Moreover, nanoemulsion’s anticancer, antioxidant, and antibacterial activities were investigated. Results: Terpinen-4-o1 (46.90%) was identified as the major compound in the essential oil. The nanoemulsion with a 149 ± 5 nm droplet size and zeta potential of -11 ± 1 mV was prepared. The cytotoxic effect of the nanoemulsion against A-375 human melanoma cells (IC50 = 139 µg/mL) showed significantly more potency than A-549 human lung cancer cells (IC50 = 318 µg/mL). Interestingly, growth of Staphylococcus aureus (Gram-positive) and E. coli (Gram-negative) bacteria after treatment with 4800 µg/mL of nanoemulsion were obtained at 12 ± 2 and 6 ± 1%, respectively. However, the IC50 value of nanoemulsion against E. coli (580 µg/mL) was not significantly different (P > 0.05) from S. aureus (611 µg/mL). Conclusion: A straightforward preparation method, high stability, and multi-biological effects are the main advantages of the prepared nanoemulsion. Therefore it could be considered for further investigation in vivo studies or complementary medicine. https://ijm.tums.ac.ir/index.php/ijm/article/view/4247 https://ijm.tums.ac.ir/index.php/ijm/article/download/4247/1601