[en] Highlights: • The hardness and strength of pure titanium fabricated by SLM were increased with increasing the laser power. • During the SLM processing, the concentrations of oxygen and nitrogen in the SLM parts were increased. • The oxidation and nitriding were thermodynamically possible under SLM. - Abstract: This study analyzed the variation of mechanical properties and its causes with increasing the laser power in the fabrication of pure titanium by selective laser melting (SLM). SLM samples were fabricated using commercially pure titanium grade 1 powder when the scan speed was 1000 mm/s and the laser power as 120, 200, 280, 360, and 440 W, respectively. As the laser power increased, the hardness and strength of the samples increased gradually. During the SLM processing, the concentrations of oxygen and nitrogen in the SLM samples were increased, which resulted in the increase of hardness and strength. The SLM equipment used in this study removed oxygen in the chamber by flowing high purity argon gas and fabricates the sample while preserving the oxygen concentration in the atmosphere to 0.2%. Evaluating the possibility of oxidation and nitriding during the SLM process by thermodynamic analysis, it was found that the process occurred under conditions in which temperature and residual oxygen and nitrogen partial pressure led to oxidation and nitriding.