 This paper investigates the microstructure and mechanical properties of a high-power laser powder bed fusion Olsi 10mg alloy before and after T6 heat treatment, revealing that the as-printed sample has a columnar grain structure and strong texture, with cellular dendrites decorated with network eutectic psi and high-density dislocations in both the Ol matrix and eutectic psi. After T6 treatment, the cellular dendrites disappear, equiaxed grains increase, and eutectic psi presents as separate plates or nanoscale particles with no nanotwings or stacking faults. The tensile property anisotropy decreases and strength ductility balance improves, while the evolution mechanisms of the microstructure and tensile properties are revealed. This article was authored by Meng Na Liu, Kai Wen Wei, Ron Senju, and others.