Abstract: Abstract: Objective To study and evaluate the antibacterial effect of different concentrations of bioactive glass on three planktonic bacteria, Streptococcus sanguis plaque and mixed plague. Methods The Minimal inhibitory concentration (MIC) and Minimal bactericidal concentration (MBC) of bioactive glass on Streptococcus sanguis, Streptococcus mutans and Actinomyces viscosus were mensurated, and the pH value was measured at the same time. Bioactive glass with a MIC concentration was cultured with bacteria broth for 10mins, 30mins and 60mins, and then followed with plate counting protocol. Field emission scanning electron microscope (FE-SEM) was utilized to observe the 24h Streptococcus sanguis plague and 48h mixed plague after 10mins’ exposure to 37.5,75 and 150mg/ml bioactive glass. The effects of bioactive glass were visualized under confocal laser scanning microscopy(CLSM).Results Low concentration of bioactive glass was effective in inhibiting the bacteria from producing acid, and a significant difference(P<0.001) in the pH value was found between the control group and the test group. As the concentration of bioactive glass rose, bacterial aggregate became smaller and thinner. Conclusion Bioactive glass is effective in killing bacteria and it has inhibitory effect on both single and mixed plague. It also shows good sterlization and anti-acid ability even with low concentration.