This study aims to investigate the effect of antimicrobial photodynamic therapy (a-PDT) using a novel combination of sinoporphyrin sodium (DVDMS) and light-emitting diode (LED) with a wavelength of 390-400 nm onPorphyromonas gingivalisin vitro. Absorption spectrum of DVDMS was determined by spectrometer for selecting suitable wavelength light source. The uptake of DVDMS byP. gingivaliswas evaluated according to fluorescence intensity detected by a spectrometer. Then effects of DVDMS alone, 390-400 nm LED alone, and photodynamic therapy produced by 10, 20, 40, and 80 mu g/mL DVDMS and 390-400 nm LED on the suspension ofP. gingivaliswere evaluated by counting the number of colony forming units (CFU) after incubation. In the experiment, the LED illumination time was 30, 60, 90, 120, 180, 240, and 360 s, respectively, and the corresponding energy density was 1, 2, 3, 4, 6, 8, and 12 J/cm(2), respectively. According to the absorption spectrum of DVDMS, the 390-400-nm light emitted by the LED was selected as the light source. The fluorescence intensity of DVDMS onP. gingivalisincreased significantly at 5 min, and with the extension of time, it decreased at 30 min. DVDMS alone did not produce a significant toxicity onP. gingivaliscompared with PBS (p = 0.979). While 390-400 nm LED alone had a certain bactericidal effect onP. gingivalis, the bactericidal effect was more obvious as the light dose increased (p < 0.001). The effect of a-PDT produced by 20, 40, and 80 mu g/mL DVDMS and 390-400 nm LED were significantly better than that of 390-400 nm LED alone (p < 0.05). Both DVDMS concentration and light dose could enchance the bactericidal effect. The strongest photo-killing effect was generated by 80 mu g/mL DVDMS with 360 s illumination (energy density is 12 J/cm(2)), and the log reduction of bacteria was 5.69 +/- 1.70. a-PDT using the combination of DVDMS with 390-400 nm LED shows promise as a new treatment modality for pathogens elimination in periodontal therapy.