Selective laser melting (SLM) was used to fabricate Hastelloy X alloy. The characteristics of grains and precipitates in Hastelloy X alloy processed by heat treatments (HT) and hot isostatic pressing (HIP) was analyzed. Furthermore, the tensile property of Hastelloy X alloys at ambient temperature and elevated temperature was investigated. Some grains exhibit columnar crystal morphology in vertically built samples, while the grains are equiaxial in horizontally built samples. The carbide phases with cubic structure are formed within grains and at grain boundaries simultaneously after a combination of HT and HIP. The horizontally built samples exhibits high tensile strength and low plasticity compared with the vertically built ones. Both of vertically built and horizontally built samples show predominantly ductile failure as characterized by dimpled microstructure. The tensile strength of Hastelloy X alloy at ambient temperature produced by SLM is 95% higher than that of hot forged alloy, while the tensile strength at 600℃ is about 85% of hot forged ones.