A single pass of half-channel angular extrusion (HCAE), an unconventional severe plastic deformation process of an Mg–3Al–1Zn rolled plate, was performed at 523K with six different starting textures with respect to three inter-perpendicular specimens along RD, TD, and ND in two types of initial plates such as as-rolled and twin-induced. In order to investigate the texture development and corresponding changes of mechanical properties, an EBSD OIM analysis and tensile tests at room temperature of HCAE-processed samples were carried out. The results show that the strength and ductility of Mg–3Al–1Zn can both be improved by controlling the initial microstructure in the HCAE process.