The paramagnetic nature of cobalt-molybdenum catalysts, synthesized on the basis of ammonium hepta­mo­lybdate or a mixture of oxobromide of molybdenum and cobalt(II) bromide has been studied by the EPR method. Hyperfine structure lines were observed in EPR spectra of these catalysts, indicating formation of stable radical complex. The conditions for preparing the catalysts notable for stable catalytic action were found. It is shown that the increase of Co content relative to Mo from 1:1 to 3:1 leads to incre­ased conversion of the substrate to 10–15% in oxidation reactions of saturated and unsaturated hydrocarbons.