Pre-reacted powders of M-type strontium hexaferrites with chemical composition Sr1−xLa 2 3 x Fe12O19 (x = 0.1, 0.2, 0.3 0.5, 0.6) were obtained from the conventional solid state reaction method. The final consolidation of these powders were performed by using the spark plasma sintering (SPS) technique. The influence of the La3+ content on the crystal structure and the magnetic properties of the samples were investigated firstly under the framework of a phenomenological model that predicted the cation substitution/distribution in the Sr and/or Fe sites. The theoretical results indicated that La3+ ion mostly occupies the Sr2+ site. It was also found that as La content increased, a certain amount of Fe2+ ions appear as a consequence of the Fe3+ to Fe2+ reduction. However, the Fe2+ occupied preferably the 12k and 4f1 iron sites. The magnetic properties of the obtained samples were assessed by measurements performed in a vibrating sample magnetometer. Also, X-ray diffraction (XRD) measurements were presented as a complementary characterization. We have found that the magnetic properties of the samples degraded as the La3+ content increased and the increase of the Fe2O3 impurity phase.