The physical properties of IN738 alloy powder prepared by the gas atomization technology are fully characterized. The particle size distributions, particle surface roughness, surface morphologies and internal structures of the powder and the selective laser melting(SLM)formed parts are analyzed. The results show that most of the IN738 alloy powder is spherical or spheroidal. The particle size distribution is normal with the powder particle sizes d10 of 14.96 μm, d50 of 28.72 μm, and d90 of 52.85 μm. The time used for 50 g powder flowing through a fluidity tester is 23.4 s. The laser absorptivity of powder increases as particle size and surface roughness increase. The surface of the SLM formed part is well lapped and the density reaches 99.3%.