The effects of magnesium oxide (MgO), calcium oxide (CaO), and zinc oxide (ZnO) powder slurries on spores of Bacillus subtilis were examined. The CaO and MgO powder slurries were able to kill the spores of B. subtilis in physiological saline. The efficacy of the CaO powder slurry was much higher than that of the MgO powder slurry. It was considered that the efficacy of the CaO powder slurry against the spores depended od effects of Ca2+ and some factors due to contact between sports and the CaO powders. When the spores and nutrients such as growth medium existed together, it was observed that the MgO, CaO and ZnO powder slurries exhibited antibacterial activity against spores of B. subtilis. There was no difference in sensitivity to the ceramic powder slurry between the vegetative cells and the spores of B. subtilis. Further, the supernatant of the ceramic powder slurries promoted the germination of the spores. Therefore, it was suggested that the ceramic powder slurries weakened a high dormancy of spores, and acted on the germinated spores.