Purpose: To compare the antibacterial activity of an adhesive system containing an antibacterial monomer MDPB, Clearfil Protect Bond with three different cavity disinfectants, chlorhexidine gluconate-based Consepsis, benzalkonium chloride-based Tubulicid Red and 3% hydrogen peroxide. Methods: Materials were tested using agar well technique and a tooth cavity model. The test materials were filled in the agar wells of plates inoculated with Streptococcus mutans. After 48 hours of incubation, the zones of inhibitions were measured in millimeters. For the tooth cavity model test, cylindrical cavities were prepared in the flat occlusal dentin of human extracted molars. The teeth were left in a broth culture of Streptococcus mutans at 37 degrees C for 72 hours allowing bacteria to invade. Teeth were then randomly assigned into five groups of five teeth (10 cavity preparations) each. In the first four groups test materials were applied into the cavities following the manufacturer's instructions and the cavities in the fifth group were left untreated for control. The teeth were kept in saline for 72 hours. Standard amounts of dentin chips were obtained from the cavity walls and the number of bacteria recovered was counted. Results: The results were analyzed by ANOVA, Dunnett C and Bonferroni tests. For the agar well technique, Clearfil Protect Bond primer exhibited greater inhibition zones than all three cavity disinfectants (P< 0.05). When tested by the cavity method, the application of Clearfil Protect Bond system resulted in significantly less bacterial recovery than all disinfectants (P< 0.05). For both microbiological methods, there were no significant differences between the antibacterial activities of Consepsis and Tubulicid Red (P> 0.05). They were superior to hydrogen peroxide in the cavity test method (P< 0.05).