© 2015 . The microstructure and mechanical properties of SLM and EBM Ti-6Al-4V samples have been compared. The effect of part size and orientation on the defects, microstructure and their contribution to the tensile and fatigue properties were elucidated. As-fabricated SLM and EBM samples mainly consisted of α' and α + β phases, respectively. Pores were the main defects in SLM and EBM samples, and closely related to scanning strategies and energy input. The porosity of SLM samples was higher compared to EBM samples. The part size had an obvious influence on the microstructure and mechanical properties of EBM samples but less so for SLM samples. Both SLM and EBM samples possessed higher strength and better ductility in the vertical orientation than those in the horizontal orientation. The tensile strength of SLM samples was significantly greater than that of EBM samples whereas the ductility was much lower. Due to the pores contained in samples, fatigue strength of both EBM and SLM samples was lower than those of cast and annealed alloys. However, hot isostatic pressing (HIP) significantly increased the fatigue limits of both SLM and EBM samples to above 550 MPa by closing of the pores.