In a previous investigation concerning the ductility of Mg-La-Zr alloys, it was revealed that the tensile-tested MgLa-Zr alloys developed ultrafine grains within the deformed areas of the specimens. On the basis of those observations, in the present study, cast Mg-La-1.5Zr alloys with lanthanum content varying between 0 and 5.4 wt.% were hot-rolled and the microstructures examined by optical microscopy, X-ray diffraction, EBSD and KAM analyses to establish the characteristics of the hot-rolled and annealed specimens. It was revealed that the microstructures within the primary and eutectic αMg of hot-rolled Mg-5.4La-1.5Zr materials consisted of fine grains of 3.6 and 0.3 μm in average size, respectively. The grain growth of these fine grains within the primary αMg did not expand into the eutectic regions during annealing, while the fine grains within the eutectic αMg remained as fine as those observed in the hot-rolled materials even after annealing at 400 ºC. This is most likely due to the proximity of a eutectic Mg12La phase that may act as an obstacle to grain growth, suggesting the possibility of developing materials with bimodal microstructures. It was also found that the level of the basal texture in the hot-rolled and annealed materials of Mg-La-1.5Zr alloys was significantly lower than that of Mg-Zr alloy, demonstrating the beneficial effects of lanthanum. Key words:Mg-La-Zr alloys, hot-rolled materials, ultrafine grains, eutectic, bimodal microstructures. 緒 言