Background: Streptococcus mutans is known as primary microorganism in the formation of dental plaque and tooth decay. Aims and Objectives: To determine the antibacterial activity of ant-nest plant ethanol extract to inhibit S. mutans clinical isolates growth in vitro. Materials and Methods: The ethanol extracts obtained from the ant-nest plant were studied for antibacterial activity against cariogenic S. mutans obtained from patients with clinically identified carious lesions, using the agar diffusion method. Chlorhexidine gluconate was using as a comparative drug. The simplisia of ant-nest plant was extracted using a maceration method. The phytochemical screening was taken using standard methods. The minimum inhibitory concentration (MIC) test was performed by a macrodilution method and following by subculturing the overnight result onto the surface of agar media. Results: Phytochemical screening of ant-nest plant ethanol extract revealed the presence of polyphenols, flavonoids, tannins, and saponins. The extract showed intensive activity and totally inhibited the growth of S. mutans clinical isolates at 1.25% w/v. In comparison, the chlorhexidine gluconate, essential oil of plants and povidone-iodine in a ranged tested concentration also had given inhibition effect to all hyaluronic acid resistant S. mutans isolates. Conclusion: It can be reasoned that the ethanolic extract of ant-nest plant gave potent and direct antibacterial effect on S. mutans.