Fe2+-, Fe3+-, and Sn4+-based complex oxides, namely, Fe2GeO4, Ca Fe2O4 and Ca2SnO4 nanopowders were prepared via single -step mechanosynthesis performed at room temperature. The mechanically induced formation of a nanooxide product phase was followed by XRD,57Fe Mössbauer spectroscopy, and NMR. It is demonstrated that the mechanosynthesis of the complex oxide can proceed very rapidly (up to 4 h). This is i n a strong c ontrast to the conventio nal solid-state synthes is of the com plex oxides, which req uires prol onged e xposure a t considerably elevated temperatures. It was revealed that the main structural features of the mechanosynthesized oxides a re nonequilibrium cation distribution and distorted oxygen polyhedra.