Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 17 5 2025 10 14 791 803 Nguyen Vinh Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, University of Health Sciences, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam; Department of Pharmaceutics, Research Center Of Discovery and Development Of Healthcare Products, Vietnam National University Ho Chi Minh City, Vietnam Nguyen Bac Department of Microbiology and Parasitology, School of Pharmacy, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam Nguyen Thien Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, University of Health Sciences, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam Do Minh Department of Science, John F. Kennedy Catholic High School, Washington, U.S.A Dao Trung Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, University of Health Sciences, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam 2025 07 15 2025 09 14 Background and Objectives: White basil (Ocimum gratissimum L. Lamiaceae) essential oil exhibits potent antibacterial effects but its aqueous insolubility and high volatility restrict its applications. This study aimed to develop a nanodispersed mouthwash containing white basil essential oil, optimizing of surfactant/co-surfactant type and ratio, assess its physicochemical stability and antibacterial efficacy against Streptococcus mutans ATCC 25175. Materials and Methods: Formulations combining white basil essential oil, Tween-80, isopropanol, Labrasol and water were prepared. Particle size, zeta potential, and pH were measured. Stability was evaluated under accelerated (40°C, 75% RH) and stressed (60°C, 75% RH) conditions over three months. Antimicrobial efficacy was assessed via minimum bactericidal concentration (MBC) after 30-second exposure. Results: Characterization of the optimized formulation revealed an average particle size of 128 nm, neutral zeta potential, pH 3.42. Stability testing demonstrated thermodynamic resistance under all storage conditions for three months without phase separation or significant size change. The MBC against Streptococcus mutans was 0.4% w/v essential oil following 30 seconds of exposure. A corresponding mouthwash with 0.4% w/v essential oil demonstrated equivalent bactericidal activity. Conclusion: Nanodispersion offers a promising strategy for white basil essential oil in mouthwash formulations. The developed formulation shows favorable stability and rapid bactericidal action, supporting further evaluation for clinical and commercial development. https://ijm.tums.ac.ir/index.php/ijm/article/view/5628 https://ijm.tums.ac.ir/index.php/ijm/article/download/5628/1825