In this study, the microstructure of hot-extruded and under-extruded Zr bearing aluminum alloys Mesoalite10 ®-1.3 mass%Zr was investigated by high-resolution EBSP analysis and the effect of Zr addition on microstructure formation during hot extrusion was studied. In an extruded Zr free alloy, coarse fibrous grains elongated to the extrusion direction were predominantly evolved. And these grains were considered to be formed by elongation of the original equi-axial grains by extrusion. Whereas, in extruded Meso10-1.3 Zr alloy, many fine grains were evolved near the grain boundaries of the fibrous grains. In under-extruded Meso10-1.3 Zr alloy, inhomogeneous local strains were developed near random grain boundaries and new fine grains were formed by continuous dynamic recrystallization. It is considered that in aluminum alloys, the addition of Zr promotes continuous dynamic recrystallization during hot extrusion.