The Fe-Al and Cu-Fe-Al oxide nanocomposites active in the oxidation of CO were studied by XRD, TEM, EDX, Raman spectroscopy, TPR-H2 and differential dissolution techniques. The nanocomposites were prepared by fusion of aluminum, iron, and copper salts that leads to their inhomogeneity. The Al3+ cations partially dissolve in the Fe2O3 lattice, which leads to a significant decrease in size of iron oxide. Copper locates in the Al-rich agglomerates to form CuO nanoparticles and partially dissolves in alumina. The dissolution of copper in iron oxide and formation of a (Cu,Al,Fe)3O4 spinel was observed only at a high Cu loading. Hence, aluminum plays the role of a textural promoter, preventing sintering and stabilization of the high specific surface area of oxide. Copper does not act as a textural promoter, as it does not affect the crystal size of iron oxide. The addition of Cu increases the catalytic activity of iron oxide-based catalysts.