In order to elucidate the antibacterial mechanisms of magnesium oxide (MgO), calcium oxide (CaO) and zinc oxide (ZnO), the generation of active oxygen from these ceramic powder slurries was examined by oxygen electrode analysis and chemiluminescence analysis. Hydrogen peroxide (H2O2) generated from the ZnO powder slurry was detected using the oxygen electrode. Active oxygen from the MgO and CaO powder slurries was not detected by the oxygen electrode analysis. Chemiluminescence analysis could detect the generation of active oxygen from three kinds of powders. The luminescence response of the CaO powder slurry was markedly strong. The chemiluminescence responses of the CaO and MgO powder slurries are due to the superoxide anion (O-2(-)). The order of the strength of luminescence response was CaO, MgO, and ZnO, which agreed with that of the antibacterial activity of these powders. These results suggested that active oxygen species generated from the ceramic powders were associated with their antibacterial activities.