Objective: To study the antibacterial effect of two commercially available bleaching agents both in vitro an in vivo. Materials and Methods: Growth inhibition study was performed to determine the effect of the test materials on Streptococcus mutans using the agar diffusion test. Zones of microbial inhibition were measured and compared. For the clinical study 30 volunteers were divided into three groups, two treatment groups and a control group. Stimulated whole saliva samples were collected at baseline, after 1 and three applications and 14 days post-treatment. Total count of aerobic bacteria was determined. Results: Growth inhibition study showed that all the three products inhibited bacterial growth, where Nite White ACP Turbo showed the statistically significantly highest mean diameter of zones of microbial inhibition. For the clinical study, there was no statistically significant difference between mean bacterial counts in the three groups, at all periods of the study. For all groups there was a statistically significant decrease in mean count of aerobic bacteria through all periods of the study. After 1 application and 3 applications, there was no statistically significant difference between mean percentage reductions in bacterial counts of the three groups. After 14 days, Nite White ACP Turbo group showed the statistically significantly highest mean percentage reduction, followed by Nite White ACP group, then the control group. Conclusion: Bleaching agents has an antibacterial effect against Streptococcus mutans in vitro, and can reduce the total count of aerobic bacteria in saliva in vivo.