We examined the presence of PpIX in P. gingivalis to investigate the possibility of 1O2 generation. The fluorescence intensity of P. gingivalis was measured using the excitation (460 nm) and emission (703 nm) wavelengths of PpIX, and the concentration of P. gingivalis and the relative fluorescence intensity increased proportionally, with a strong correlation (Fig. 3A). The observed correlation with the relative fluorescence intensity of P. gingivalis (Fig. 3B) suggested the presence of a photosensitizer like PpIX in P. gingivalis cells. Due to the presence of the photosensitizer-like pigment, we chose to investigate the effects of blue light irradiation on P. gingivalis. A decrease in the viability of P. gingivalis was observed with 10 and 100J of blue light irradiation (Fig. 4).