The thermal behavior of double-complex salts [Cr(ur)6][Fe(CN)6]·4H2O (I), [Cr(ur)6][Co(CN)6]·4H2O (II), [Cr(ur)6][Fe(C2O4)3]·2H2O (III), [Cr(ur)6][Co(C2O4)3]·3.5H2O (IV) was studied (ur = urea, H2NCONH2). Thermal decomposition was carried out by the method of static experiments in an oxidizing (air) atmosphere at a 1-h exposure. The products of thermolysis were characterized by the X-ray diffraction method. The porous structure and the specific surface of the samples were determined. For Cr–Co systems at temperatures above 600 °C, the formation of a single-phase spinel of the composition Co1.5Cr1.5O4 was recorded, whereas for the Cr–Fe systems the formation of a mixed oxide phase (Fe,Cr)2O3 occurred with heating up to 900 °C. It was shown that in all cases, as the temperature increased, the specific surface area decreased and the calculated particle size of the oxidation products increased. Thermolysis products were investigated in the model reaction of catalytic oxidation of acetone with air oxygen. The obtained values of the rate constants of the reaction show that the replacement of Fe with Co does not significantly affect the catalytic activity of the products, and only an increase in the temperature of thermolysis leads to a certain decrease in the catalytic activity.