Caries is a multifactorial infection that can be caused by Streptococcus mutans. This bacteria is responsible for the formation of oral biofilms and incorporates properties that is conducive for its survival in hostile oral environments. Long-term adverse effects like hypersensitivity reactions, supra-infections and teeth staining coupled with the risk of resistance-development limit use of chemical preparations and antibiotics for caries prevention. Hence plant-based formulations with substantial antimicrobial and anti-cariogenic properties, could serve as alternatives for caries prevention. In this study, a Cymbopogon citratus (lemongrass) oil-in-water emulsion with Tween80/Span80 was formulated and favorably characterized using particle size (252.3±1.15nm with polydispersity index of 0.111± 0.01), FTIR and AFM analyses and stability studies. Its MIC and the MIC of alumina nanoparticles against cultures and isolates of Streptococcus mutans was around 600ppm. However, with the alumina nanoparticle loaded emulsion, the MIC was observed at a much lower concentration of around 400ppm. This nanoparticle incorporated emulsion was also able to inhibit the biofilm formation, with t he time kill assay showing a decrease in cell numbers within 60 to 120 minutes post incubation. Alumina incorporated lemon grass oil emulsion may thus to prevent dental caries induced by Streptococcus mutans. © RJPT All right reserved.