Dental caries is one of the dental and oral health problems that still need attention in Indonesia. Lactobacillus acidophilus has a role in the caries process. Lactobacillus acidophilus can advance a progressive lesion caries and produce lactic acid as an end product of fermentation from carbohydrates, which is acidic in nature cariogenic. The acid formed can soften the hardest part of the tooth is the enamel. Myrmecodia pendens Merr. & Perry is one of the herbs that have been used as medicine such as for ulcer, haemorrhoid, allergies, tumors, cancer, and it has the antioxidant content as well as antiinflamation. Ant-plant has polyphenols, tannins, tocopherols, and flavonoids potential as an antimicrobial. Research objective: This research aimed to find out the effects of antibacterial power of ethanol extract mouthwash from Myrmecodia pendens Merr. & Perry to Lactobacillus acidophilus. Research methodology: This research was designed using purely laboratory experiment. Cultured Lactobacillus acidophilus was incubated with ethanol extract mouthwash from Myrmecodia pendens Merr. & Perry with concentration of 10%, 25%, 50%, 75%, dan 100% for 18-24 hours within the temperature of 37°C with 4 controls that are positive control was using of Chlorhexidine gluconate 0.2%, negative control was the basic formula of mouthwash (0% concentrate), control bacteria, and control media. The antibacterial power test was using liquid dilution method to determine the minimum inhibitory concentration (MIC) and solid dilution to determine the minimum bactericidal concentration (MBC). The data were analyzed using descriptive quantitative methode. Research findings: The result of this research shows that ethanol extract of mouthwash from Myrmecodia pendens Merr. & Perry has minimum inhibitory concentration (MIC) at a formula I (concentration 10%) and minimum bactericidal concentration (MBC) at a formula II (concentration 25%). Conclusion: Ethanol extract mouthwash from Myrmecodia pendens Merr. & Perry has antibacterial power to Lactobacillus acidophilus.