Single-phase powders of LaMnO 3 and LaCoO 3 , lanthanum-based perovskites, were synthesized using the citric acid combustion method. The surface concentration of La in the obtained powder was higher in LaCoO 3 than in LaMnO 3 . These samples decomposed 2-naphthol in water in the dark. The decomposition reaction is attributed to the Marsvan Krevelen (MvK) mechanism because of the temperature dependence, activation energy, valence change during the reaction, and the amount of ion elution into water. A disproportionation reaction was confirmed for Mn in LaMnO 3 . Both samples exhibited antibacterial and antiviral activity against Escherichia coli, Staphylococcus aureus, bacteriophage Q¢, and bacteriophage ¯6. The antibacterial activity was higher than the antiviral activity. LaCoO 3 tended to have higher antibacterial and antiviral activity than LaMnO 3 had. Results show that these materials had less ion leakage than that reported earlier for La 2 Mo 2 O 9 .