The aim of the study was to investigate the antibacterial activity of refined Sunflower oil, Tween 20 (polyoxyethylene (20) sorbitan monolaurate), water microemulsion system. Pseudo-ternary phase diagram was constructed to obtain the concentration range of oil, surfactant and water. Three microemulsion formulations were prepared, of which oil, tween 20 and water were made to 100 %. Conductivity and pH were used to characterize microemulsion. The concentration of refined sunflower oil varied from 5% to 15 %, the surfactant concentration varied from 10 % to 30 % and water concentration varied from 55 % to 85 %. When water concentration increases, conductivity of the microemulsion system increases upto 50 % of water concentration and after that become stable. When oil and surfactant concentration was increased, pH of the microemulsion system decreases. Kinetic studies showed inhibition of bacterial growth in all formulated microemulsions. Bacterial growth was enhanced in the case of oil and surfactant alone.