Mg–3%Al–1%Zn (AZ31) alloy was subjected to ECAE (Equal Channel Angular Extrusion) processing under various processing conditions in order to reveal the effect of the microstructural parameters on tensile properties of magnesium alloy. Then tensile tests were carried out at room temperature to investigate the relationship between tensile properties and microstructural parameters including the texture generated by ECAE processing and grain size. As a result, in 4–pass ECAE specimens processed at 250°C, tensile ductility is improved as a result of basal slip that occurs easily when tensile test was performed along the extrusion direction, because such specimens have textures in which the basal plane is inclined at 45° to the extrusion direction. On the other hand, in the specimens processed at 300°C, which have textures in which the basal plane is oriented parallel to the extrusion direction, 0.2% proof stress is higher than those of specimens processed at lower temperatures, but elongation is smaller because basal slip is difficult to occur. However, 8-pass specimens processed at 200°C and annealed, which have similar texture but different grain sizes (d) exhibit clear grain size dependencies of 0.2% proof stress (σ_0.2) according to Hall-Petch relationship; σ_0.2 = 30 + 0.17d^−1⁄2. Therefore, crystallographic orientation has a profound effect on the tensile properties of AZ31 alloy, and grain size also has a little effect.