The catalytic activities of NiMnO3 and NiMn2O4 during heterogeneous catalytic decomposition of ozone and ozone-catalytic oxidation (OZCO) of benzene at low temperatures (20-80 degrees C) have been investigated. The sensitivity of the two oxides towards strong catalytic poisons, such as nitrogen oxides, during the decomposition of ozone has also been estimated. On the basis of the experimental results obtained it is concluded that the NiMnO3 and NiMn2O4 obtained have a high activity with respect to the reactions of ozone decomposition and CO and CH oxidation in the presence of ozone at temperatures close to the room temperature. The sample with an ilmenite structure shows, in all cases, a higher catalytic activity. The surface oxygen of NiMnO3 is more reactive at room temperature than is the case of NiMn2O4. The hypothesis according to which when the two metal cations are in octahedral coordination the catalyst activity is higher and the stability towards catalytic poisons is enhanced has proved to be correct. It should be noted that a catalyst has been synthesized which is able to decompose ozone at room temperature and to activate the organic molecule to a de,sree permitting catalytic oxidation by ozone at room temperature. In addition, this catalyst shows a relatively high stability with respect to poisoning by nitrogen oxides.