<p>The influence of building orientations on the fracture toughness and fatigue crack growth (FCG) behaviors of selective laser melting Ti-6Al-4V alloy has been investigated in the present paper. Standard compact tension samples with cracks propagating parallel and normal to the plane of substrate were manufactured with the stress relieving and hot isostatic pressing (HIP) heat treatment. Microstructure was discussed to elucidate its effect on the fracture toughness and FCG behaviors. It was found that the alloy has an <i>α</i>/<i>β</i> phase mixture, and the lamellar <i>α</i>-phase occupies more than 90%. Different building orientations bring significant anisotropy to both the microstructure characterization and mechanical properties. Through the comparison between the thickness of laths in two groups of parts on the plane normal to crack extension, it was indicated that the specimen with coarser <i>α</i>-phase laths has higher fracture toughness and FCG near-threshold value. Building orientation plays a trivial role in FCG rate when the stress intensity factor range (<i>ΔK</i>) of 12&#xa0;MPa•m^0.5 ~ 20&#xa0;MPa•m^0.5. The FCG and fracture toughness data are comparable or even exceed those of mill-annealed wrought material. In summary, the prior-<i>β</i> grain characteristics with lamellar and basketweave microstructure, especially the thickness of the <i>α</i> laths, are critical factors that contribute to the anisotropic fracture toughness and FCG properties.</p>