Selective laser melting (SLM) as an additive manufacturing technology enables the quick production of complex shaped three-dimensional (3D) specimens directly from a metal powder. Various metal powders, including different steels, are used in this technology. The influence of the SLM process on the phase composition of the final 3D specimen has been examined by Mössbauer spectroscopy (MS) The surface quality has been examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The maraging steel 1.2709 (CL50WS), an iron-nickel steel alloy, which is often used in applications where high fracture toughness and strength are required has been investigated. The difference between the phase composition of the initial CL50WS powder and the final specimen identified via MS demonstrated transformation of a martensitic phase into an austenitic one. This transformation proceeds during the whole SLM process. SEM presented imperfections of the surface of the final specimen. The spherical and irregular pores were observed as well as the particles of initial powder bonded to face. Inhomogeneity of elements on the face has been observed by EDS.