The growth inhibitory effect of 26 ceramic powder slurries on bacteria was evaluated by measurement of the conductance change of the growth medium caused by bacterial metabolism (conductance method). Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis were used as test bacteria. It was found that the growth of the test bacteria was Inhibited by 10 ceramic powders. Magnesium oxide (MgO) and calcium oxide (CaO) powder slurries had a growth inhibitory effect on ail test bacteria. In the cases of MgO and CaO powder slurries, there was no difference in sensitivities among the test bacteria. These powder slurries exhibited bactericidal action on the test bacteria. On the other hand, the zinc oxide (ZnO) powder slurry inhibited the growth of Gram-positive bacteria stronger than Gram-negative bacteria. The effect was bacteriostatic action. The conductance method could provide quantitative and simple evaluation of the growth inhibitory effect of ceramic powder slurries on bacteria, and was more applicable than the conventional methods, such as the halo test.