This thesis investigates the structure, surface treatments, and corrosion behaviour of the 3D printed magnesium alloy WE43, prepared using the (SLM) method. The surface of the printed structure exhibited adhered particles and resublimated magnesium, leading to increased roughness and open porosity. Selected etching solutions were tested to remove surface impurities and unmelted powder particles from the structure's surface. Chemical etching was deemed unsuitable due to excessive etching, corrosive attack on the base material or insufficient surface cleaning. Electrolytic etching in 10% HClO4 in ethanol for 5 minutes proved to be the most effective method. Subsequently, a PEO coating with a thickness of approximately 3.5 μm was prepared on the samples, consisting primarily of magnesium oxide with a minor fraction of phosphates. The coating exhibited a typical porous structure with the presence of cracks. Corrosion tests in Hank’s solution proved significantly lower corrosion resistance in uncoated samples, which experienced rapid formation of corrosion product layers, development of pitting corrosion, and gradual structural disintegration. In contrast, the PEO coating significantly slowed the corrosion process and reduced hydrogen evolution; however, local failures occurred, particularly in geometrically complex areas. Long-term exposure also led to coating degradation and subsequent attack on the substrate. It was found that the PEO coating effectively resists corrosion and extends the service life of the 3D-printed structures, though the quality of the surface preparation remains a key factor.