An effective method has been developed to improve the formability of Al-Mg alloys by adding scandium as an alloying element, taking advantage of its unique precipitation hardening characteristics. In the present investigation, the development of superplasticity in an Al–5%Mg–0.3%Sc alloy was considered. Standard casting routes followed by thermomechanical treatment were employed to obtain the alloy in the sheet form with uniform, fine grain structure. A refined microstructure of Al–Mg–Sc alloy sheet was produced by simple hot forging and cold rolling to an average grain size of 10 μm. Tensile tests were performed at temperatures ranging from 748 to 823 K and initial strain rates ranging from 1 × 10−4 to 1 × 10−2 s−1. The alloy exhibited substantial deformation at the conditions of testing. Experiments were completed in a microprocessor-controlled electromechanical screw-driven testing machine, and results were investigated by means of optical microscope (OM) and scanning electron microscopy (SEM). A maximum elongation of 212% was obtained at 823 K and 1.04 × 10−4 s−1. In addition, the scanning electron microscopy (SEM) analyses showed that the presence of Al3 (Sc) particles in pinning grain boundaries and dislocations had a great influence on the superplastic deformation. Metallographic and fractographic studies were carried out on the deformed specimens and the results reported. The data interpreted that the dominant deformation mechanism was grain boundary sliding controlled by lattice self-diffusion. © 2017, Springer-Verlag London Ltd.