Objectives: - This study was conducted to evaluate the antibacterial activity of titanium dioxide nanoparticles that incorporated into; resin composite, adhesive, and both. Materials and methods: 10 wt% titanium dioxide nanoparticles (TiO2NPs) were incorporated into resin composite and adhesive to obtain modified resin composite and adhesive. Forty patients have Class V caries were selected to receive composite restorations. Class V cavities were prepared and divided into 4 groups according to the incorporation of titanium dioxide nanoparticles into the restoration; group A1 (Resin composite incorporating TiO2NPs), group A2 (adhesive incorporating TiO2NPs), group A3 (Both resin composite and adhesive incorporating TiO2NPs), and group A4 (Composite restoration free of TiO2NPs). Plaque samples were collected from the gingival margin of the restoration immediately, 1 week, and 1 month after the restoration, then colony forming units (CFUs) were counted to evaluate the count of streptococcus mutans in plaque samples. Results: There was a statistically significant reduction in CFUs count with all restorations incorporating TiO2NPs as compared to the control group. After 1 week of composite restoration, there was no statistically significant reduction in CFUs count as compared to immediately after the restoration, whereas, there was a statistically significant reduction in CFUs count after 1 month. Conclusions: Composite restorations incorporating TiO2NPs enhanced the antibacterial activity especially that blended TiO2NPs in both resin composite and adhesive. There was time dependent improvement in the antibacterial activity of composite restorations incorporating titanium dioxide nanoparticles.