Abstract: Currently, research on the preparation of GH5188 alloy using selective laser melting (SLM) is relatively scarce. GH5188 alloy was prepared using SLM technology. The microstructure and mechanical properties of the alloy in as-built and hot isostatic pressing/heat treatment (HIP/HT) states were systematically investigated. The influence mechanism of HIP/HT on the anisotropy of microstructure and properties was analyzed. The results show that the HIP/HT leads to the elimination of defects such as cracks and porosity in as-built GH5188 superalloy, the maximum relatively density reaches 99.9% and the directional distributed micro-size cell structure transforms into the homogeneous equiaxed grains containing annealed twins. In room temperature tensile test, compared with that of the as-built alloy, the elongation of the alloy after HIP/HT increases by 13.5% and 27.2% in the Z and XY directions, respectively, and the dispersion of elongation decreases from 36.3% to 4.3%. In high temperature tensile test at 980 ℃, the yield strength and ultimate tensile strength of the alloy in HIP/HT state are similar with the as-built alloy, whereas the elongation increases by 21.7% and 37% in the Z and XY directions, respectively, and the elongation dispersion decreases from 46.8% to 5.5%. This is attributed to the fact that the HIP/HT effectively eliminates the cracks and pore defects in as-built alloy and forms a homogeneous equiaxed grain structure. Meanwhile, the formation of annealed twins improves the work hardening ability of the alloy. Therefore, the HIP/HT of as-built GH5188 superalloy achieves the optimization of microstructure and mechanical properties as well as the elimination of anisotropy.