The plastic anisotropy was measured for a commercial AZ31 magnesium sheet and compared with results from a model calculation using a self consistent viscoplastic model. The anisotropy of plastic flow stresses can be explained by the off-basal character of the texture and the activation of the < a > prismatic slip in addition to the basal, < c+a > pyramidal slip and the {0112} < 0111 > twinning system. The strain anisotropy r (r = epsilon(w)/epsilon(t); epsilon(w), epsilon(t) - strains in width and thickness directions of a sheet material), as obtained from model calculations, fits qualitatively with in-situ measured values. Results from these model calculations are compared with texture simulations and discussed in further consideration of the microstructure of the sheet material.