To investigate effective methods to sterilize a biological safety cabinet contaminated with Bacillus spores, a sterilization study was performed using the vaporized KMT reagent. Five kinds of test carriers inoculated with Bacillus subtilis spores, which had been prepared in-house, were used as indicators. The KMT reagent was placed in the middle of the work-area (1.2 m-wide, Class II type A cabinet). Approximately 300 ml of vaporized KMT reagent could bring about complete sterilization of this cabinet by 24 h of exposure without severe corrosion. Vaporized KMT reagent could be used for the safe and easy sterilization of cabinets contaminated with Bacillus spores.