The oxidation kinetics of a porous Si2N2O-ZrO2 composite material are investigated. Samples were oxidized at different temperatures between 1000 and 1450 degrees C. Transmission electron microscopy was used for investigations of the formed oxide layer. Samples of pure Si2N2O and reaction couples of ZrO2/SiO2 were prepared by a thin-film technique and heat-treated at 1250 and 1350 degrees C, respectively. The thickness of the formed reaction layers was determined by spectroscopic ellipsometry. The formation of amorphous silica on Si2N2O was found to be faster than on Si, and this may have significant impact on the oxidation rate of the composite material. At 1350 degrees C, ZrSiO4 starts to form considerably in the ZrO2/SiO2 reaction couple and may retard further oxidation in the composite material. This process is favored at higher temperatures.