We have fabricated fully released nano-electro-mechanical system (NEMS) cantilevers of various geometries from metallic alloy nanocomposite films. At thicknesses of 4.3 and 20.0 nm, these are the thinnest released metal cantilevers reported in the literature to date. Such device dimensions are very difficult to achieve using conventional metal films. We were able to overcome this limitation by using room-temperature co-sputtering to synthesize nanocomposite alloy films of Al–Mo. A systematic investigation of microstructure and properties as a function of Mo content resulted in an optimum film composition of Al–32 at.%Mo with a unique microstructure comprising a dense distribution of nano-scale Mo crystallites dispersed in an amorphous Al-rich matrix. These films were found to exhibit unusually high nanoindentation hardness and a very significant reduction in roughness compared with pure Al, while maintaining resistivity in the metallic range. A single-anchored cantilever 5 µm long, 800 nm wide and 20 nm thick showed a resonance frequency of 608 kHz, yielding a Young's modulus of 112 GPa, in good agreement with a reduced modulus of 138 GPa measured by nanoindentation.