The effect of Sc on plasticity at elevated temperatures(from 300 to 500 °C) and strain rates(from 10−3 to 10−1 s−1)of ultrafine-grained (UFG) Al–0.5%Mg–Sc alloyswas investigated. In the UFG alloys with 0.4% and 0.5%Sc at 500 °C and strain rate 1·10−1 s−1, high elongation to failure (~1060%) was achieved. The fractographic analysis of the fracturesin the Al–0.5%Mg alloy demonstrated the crack growth zone to occupy almost whole fracture area.The self-destruction in the crack growth zone has a viscous character.In the UFG alloys with Sc, numerous pits formed as a result of micropore junction were observed. Dependencies of dynamic grain growth (DGG) rate on the temperature and strain rate were determined. The DGG in the Al–0.5%Mg–Sc alloys was found. The kinetics of the DGG in the Al–0.5%Mg–0.2%Sc alloy was shown to be limited by mobility of junction disclinations. In the Al–0.5%Mg–0.5%Sc alloy, it is limited by mobility of oriented misfit dislocations. Al3Sc particles were shown to be possible origin of the micropore formation and of accelerated destruction of the Al–0.5%Mg–Sc alloys at high temperature deformation. •Al–0.5Mg–Sc UFG alloys have high superplastic characteristics.•A dynamic grain growth (DGG) with the exponent k=∂lg⁡(ḋ)/∂lg⁡(ε̇) = 0.8–1.3.•The DGG rate in the alloys with low Sc content is governed by the mobility of the joint disclinations.•The DGG rate in the alloys with high Sc content is governed by the mobility of the orientation mismatch dislocations.•A formation of pores takes place on the Al3Sc particles in the tensile state.