Two nanocomposite oxides, NiO/Co₃O₄ and CuO/Co₃O₄, have been considered. These nanocomposite oxides of (1-x)NiO/xCo₃O₄ and (1-x)CuO/xCo₃O₄ with different contents of (x = 30, 50 and 70 wt%) have produced successfully using microwave irradiation. The resulted powders of pure and mixed nanoparticles (NPs) have been characterized by thermogravimetry (TGA), differential thermal analysis (DTA) and x-ray diffraction (XRD). It can be observed in TGA that the mass loss end of Co₃O₄, NiO and CuO NPs is at three stages until reach to the decomposition of Co(OH)₂, Ni(OH)₂ and Cu(OH)₂, respectively. The process of mass loss is confirmed by endo- and exo- thermic peaks in DTA thermogram. The structural properties of these nanocomposites have been studied. The XRD result confirmed the formation of pure NPs as well as the nanocomposites of NiO/Co₃O₄ or CuO/Co₃O₄ NPs. Size of nanocomposites dependence on both type and concentrations of dopant have been studied. The formation of p-p type has been confirmed by structural investigations.