Typically, magnesium alloys with conventional grain size exhibit microplastic behaviour already at low stresses. This behaviour restricts the technological utilization of these materials. The aim of this study was to investigate whether ECAP can be applied to enlarge the elastic range of AS21X. Cyclic tensile tests at room temperature were carried out to examine the effect of the ECAP induced grain refinement on the elastic properties. The results obtained are compared with the cyclic behaviour of conventional, coarse-grained AS21X. The differences in mechanical properties between the two conditions are discussed.