〔Abstract〕 Objective To study the antibacterial effect of a new photosensitizer NHS-BODIPY-Br on the biofilm ofP gingivalisandT forsythia in vitro. Methods The biocompatibility of photosensitizer NHS-BODIPY-Br was detected by CCK8.P gingivalisandT forsythiawere cultured in anaerobic condition(10% CO2,10% H2,80% N2) for 48 h to form a biofilm and then treated with antibacterial photodynamic therapy.The photosensitizer concentration was 5,10,15 mg/L and the laser intensity was 15 and 30 J/cm2.After treatment, bacterial activity, residual LPS and laser confocal analysis were performed to determine the optimal treatment combination. Results The reduction rate ofbacterial biofilm was about 98%when the concentration of NHS-BODIPY-Br was 10 mg/L and the laser intensity was 15 J/cm2. Conclusion This study shows that the NHS-BODIPY-Br-mediated photodynamic therapy can effectively inhibit the biofilm ofP gingivalisandT forsythia.