Objectives:The minimal bactericidal concentration (MBC) of Java turmeric (Curcuma xanthorrhiza Roxb.) ethanol extract is 25% against Streptococcus mutans and 15% against Streptococcus sanguinis as single species. This study aimed to examine the antibacterial effect of Java turmeric ethanol extract against S. mutans and S. sanguinis as dual-species. S. mutans and S. sanguinis compete against each other to obtain nutrients. Methods:The antibacterial effect of Java turmeric ethanol extract against dual-species Streptococcus in vitro was analyzed by measuring the growth of bacteria after exposure to the extract by counting colony formation and quantifying bacterial cell numbers using real-time polymerase chain reaction. Result:The MBC of Java turmeric ethanol extract against dual-species Streptococcus is 10%. S. sanguinis is more sensitive to the extract than S. mutans. Conclusions:The antibacterial effect of Java turmeric ethanol extract on S. mutans and S. sanguinis as single species differs from the effect on the bacteria as dual-species of Streptococcus.