The effect of an ultrafine-grained (UFG) structure formed in an aluminum alloy 1570 using severe plastic deformation by high-pressure torsion (HPT) at room temperature and at temperatures of 100 and 200°C on the mechanical properties (strength and plasticity) has been investigated. The specific features of the UFG states obtained have been studied by transmission electron microscopy and X-ray diffraction analysis. The main regularities of changes in the structure characteristics of the alloy (the average grain size, size of coherent domains, magnitudes of microdeformations of the crystal lattice, dislocation density, and the lattice parameter) have been established depending on the temperature of the HPT treatment. The mechanical properties of the alloy after HPT have been estimated from the results of microhardness measurements and mechanical tests for tension. It has been established that after HPT performed at room temperature, the UFG alloy demonstrates an ultimately high level of strength (the microhardness, offset yield strength, and ultimate strength reach 2300, 905, and 950 MPa, respectively) and a marked plasticity (the relative elongation at fracture was 4.7%). The HPT treatment performed at higher temperatures insignificantly reduces the strength characteristics of the UFG material but leads to a substantial drop in its plasticity. This unusual mechanical behavior of the UFG alloy is discussed based on an analysis of the results of structural investigations.