The ECAP-induced changes in grain size and grain size distribution in as cast magnesium alloyss AZ80 and ZK60 were measured by transmission electron microscopy while changes in dislocation density and crystallographic textures were determined by positron annihilation spectroscopy and X-ray diffraction analysis, respectively. The strain induced by ECAP was found to influence the microstructure characteristics, in particular the grain size, the dislocation density, and the crystallographic texture.