A study was conducted to demonstrate superstrength of ultrafine-grained (UGF) aluminum alloys produced by severe plastic deformation. It was demonstrated that UGF materials with a grain size of 100-1000 nm manifested strength properties considerably higher than those predicted by the Hall-Petch relationship extrapolated into the region of ultrasmall grains. The nature of the manifestation of this effect connected with the state of grain boundaries in these materials was considered. An analysis by the method of transmission electron microscopy (TEM) showed that the initial coarse-grained structure of alloys 1570 and 7475 was completely transformed into a UFG homogenous structure as a result of HPT. It was established by X-ray diffraction (XRD) that after HPT the lattice parameter a of the alloy 1570 decreased substantially, approaching the lattice parameter of pure aluminum.