Ultraviolet-light emitting diodes (UV-LEDs) have garnered attention for their efficient bacterial inactivation. However, in previous studies, it has been difficult to strictly compare the bacterial inactivation effect of UV irradiation among wavelengths differing by a few nanometers because detailed UV irradiation conditions for comparison, such as the LED characteristics at each wavelength and power supply characteristics, have not been established. Therefore, this study aimed to evaluate UV inactivation of 10 bacterial strains across 13 wavelengths (250-365 nm) using a standardized irradiation system previously reported to identify the most effective wavelengths for prevention of bacterial infection and contamination. Bacterial inactivation dose response curves were generated to determine the fluence required to archive 1-3 log inactivation. The results indicated that Gram-negative bacteria exhibited higher initial sensitivity compared with Gram-positive bacteria. Wavelength-dependent inactivation peaked at 263-270 nm, correlating strongly with cyclobutane pyrimidine dimer production (r > 0.9 for most strains). Deconvolution analysis confirmed that bacterial inhibition was maximal around 267.6 nm. Furthermore, UV-LEDs outperformed low-pressure mercury lamps in terms of bacterial inactivation under equivalent fluences, attributed to differences in spectral emission profiles. These findings will help optimize UV-LED sterilization methods for broader applications in microbial control.