Abstract: Martensitic aging stainless steel, known for its excellent plasticity and workability, is a vital material in aerospace applications. Additive Manufacturing (AM), particularly Selective Laser Melting (SLM), is widely used for producing complex aerospace components. However, large oxide inclusions can significantly degrade the mechanical properties of SLM parts. This study investigates the effects of adding deoxidizing elements Ti and La to powders on the properties of additively manufactured martensitic stainless steel. Four different powders were prepared and tested under various SLM process parameters. The addition of Ti and La reduced oxide size and density, improving tensile strength. These findings offer insights for controlling oxides in additively manufactured martensitic stainless steel, making them harmless or beneficial.