The microstructure and mechanical properties of ultrafine-grained (UFG) aluminum alloy Al5083 in different structural states were investigated. The UFG structure was formed by high-pressure torsion (HPT) technique. The UFG alloy exhibits high value of ultimate tensile strength (~ 725 MPa) but no ductility. Short-term annealing at 473 K and additional deformation by HPT to 0.25 of revolution at room temperature resulted in a slight decrease in material’s strength to ~ 653 MPa, which was ∼ 90 % of the value after HPT processing but provided ductility ∼ 2 %. Microstructure evolution during deformation heat treatment was investigated by transmission electron microscopy and X-ray diffraction analysis. Physical mechanisms to improve plasticity in correlation with microstructure evolution is discussed.