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Abstract. Hot isostatic pressing (HIP) with two different temperatures of 1100○ C/160MPa/2h and 1175 ○ C/160 MPa/2 h was performed on Hastelloy X samples produced by selective laser melting (SLM) was performed. The effect of hot isostatic pressing on defects, microstructures and mechanical properties of SLM fabricated Hastelloy X samples were investigated. It showed that cracks and micro-pores on within SLM-fabricated samples were gradually eliminated with the increase of HIP temperatures, increased A in which nearly fully dense part can be achieved at hot isostatic pressing of 1175 ○ C /160 MPa/2 h. The microstructure evolution rule as follows: cellular crystal in both horizon and vertical directions, no precipitates (as-deposited) → equiaxed crystal with size of 10-50 μm in horizon direction and columnar crystal with size of 200μm in vertical direction, chain-like precipitates distributed at grain boundaries (1100 ○ C/160 MPa/2 h HIP processed) → equiaxed crystal with size of 150 μm in both horizon and vertical directions, plate-like precipitates distributed at grain boundaries with size triple increased (1175 ○ C/160 MPa/2 h HIP processed). Ductile fracture occurred in both SLM deposited and HIP processed samples during room temperature tensile tests, while all tested samples behaved higher mechanical properties than traditional wrought parts. The room temperature tensile properties of the as-deposited and the two HIP processed samples all reached the standard for wrought Hastelloy X. Moreover, the ductility of HIP processed samples enhanced and tensile properties decreased compared with SLM deposited samples.