An Al-3wt.%Mg-0.2wt.%Sc alloy was subjected to equal-channel angular pressing (ECAP) through 8 passes via the processing route Bc to refine its grain size. Constant stress creep tests in compression were conducted at 473 K on ECAP billets and, for comparison purposes, on unpressed material. The present results were compared with the results of our earlier work on compressive creep of pure ECAP aluminium with the same imposed strain and the ECAP processing route. The results demonstrate that the creep strength of an Al-Mg-Sc alloy is significantly improved compared to that of pure aluminium. The higher strength observed for the pressed ternary alloy in the high-stress region (> 25 MPa) results from the synergism of solid-solution strengthening and precipitate strengthening due to Al3Sc nanoscale precipitates. The presence of these precipitates dramatically increases the creep resistance in the low-stress region through a threshold stress for creep. However, the creep resistance of the ECAP processed material was markedly deteriorated with respect to unpressed one.