Electron Beam Melting (EBM) additive manufacturing process has been developed for the manufacture of Ti6Al4V parts for the aerospace industry. In the additive manufacturing research team from Airbus Group this technology is being evaluated with a view to production of flight hardware. During the evaluation of the process, the microstructure formation was studied. It was seen that a distinctive microstructure is observed up to 0.5mm of part surface (the skin layer) and the thickness of the primary columnar ?-grains varies depending on the thickness of the parts being produced. With the purpose of quantifying the influence of the grain thickness and the mechanical performance of the material, cylinders with 9 different diameters (6mm up to 40mm diameter) were manufactured with 80mm height. The top 20mm of each cylinder was used for microstructure evaluation and the bottom 60mm was used for manufacturing a tensile specimen from the core of each cylinder. The influence of the skin layer on mechanical properties was investigated by tensile testing. The microstructure characterization showed how the grain thickness changes from thin to thick structures and the influence of grain size on tensile strength was quantified.