Equal-channel-angular-extrusion(ECAE was conducted to an Al-4Mg-0.5Sc alloy at two elevated temperatures of 473 and 673 K. The effect of processing temperature during heavily straining was investigated. Microstructural examinations revealed the formation of fine-grained(∼ 0.5 μm) structure at a low operating temperature of 473K, whereas a coarse-grain(∼ 25 μm) was formed at 673 K. The material processed at 473 K exhibited the lower flow stress with higher ductility and high strain rate sensitivity of 0.5 indicating the dominant deformation mechanism was grain boundary sliding. Finer grain structure exhibited the high-strain-rate superplasticity can be obtained at the lower processing temperature. The results indicate that the operating temperature has highly influenced the ECAE process.