The thermal behavior of double complex compounds (DCC) [Cr(ur)6][Fe(CN)6]·4Н2О (I), [Cr(ur)6][Co(CN)6]·4Н2О (II), [Cr(ur)6][Fe(C2O4)3]·2Н2О (III), [Cr(ur)6][Со(C2O4)3]·3.5Н2О (IV) and urea were studied by the TG-MS method in a reducing atmosphere. According to the results of the TG study DCC II, containing CN-, begins to decompose at a temperature ~ 50 °C higher than in the case of DCC IV with C2O42-. The reduction process finishes at ~ 520°С for all Co-containing DCC. The final solid products were mixtures of Cr2O3, Со0 (fcc and hcp modifications) for DCC II and IV; Cr2O3, Fe0 with a small admixture of Fe2O3 for I and FeCr2O4, Fe0 for III. We explain the presence of oxide phases of Fe2O3 and Cr2O3 in products of thermal decomposition by the oxidation by air oxygen of finely dispersed metal particles, witch formed during there ductive thermolysis of DСC. Urea degradation products (NH3 and HNCO) and the conversion products of the anion ligands (HCN in the case of cyanides and a mixture of CO and CO2 in the case of oxalate) are found in the gaseous products of the reduction of DCC II and IV. Insignificant amounts of nitrogen and hydrocarbons CxHy (where x≤1) are also fixed. The final products of thermolysis were tested in a model decomposition reaction of H2O2. Products of reduction of iron-containing DCC were found to have little catalytic activity. Perhaps this can be explained by the greater catalytic activity of Co0 compared to Fe0. An increase in the final thermolysis temperature leads to a decrease in the specific surface area, probably due to an increase in particle size during sintering and removal of carbon. The replacement of the ligand C2O42- by CN- leads to an increase in the products by a factor of 2.