We compared methylene blue (MB)-mediated photobactericidal efficacies against Pseudomonas aeruginosa when using nanosecond pulsed light and CW light. In the intensity range of 10-200 mW/cm 2, there was no significant difference between two cases, while photobactericidal efficacy with nanosecond pulsed light was significantly lower than that with CW light at an intensity of 250 mW/cm 2. This is attributable to the saturated absorption of MB molecules due to high peak intensity of nanosecond pulsed light. On the basis of these results, we estimated the depth dependence of bacterial killing, showing that in the skin tissue region deeper than 1.5 mm, photobactericidal efficacy with nanosecond pulsed light was higher than that with CW light. This suggests that the advantage of using high-peak-intensity pulsed light for deep tissue treatment.