The tensile mechanical properties in three mutually perpendicular directions of Inconel 718 superalloy sample fabricated by laser rapid forming (LRF) are studied. The influences of heat treatment on both the solidification microstructures of and the tensile mechanical properties in three mutually perpendicular directions of Inconel 718 superalloy sample are investigated. It is shown that the tensile mechanical properties of all test specimens are clearly inferior to that of wrought Inconel 718 superalloy. After being heat treated, the coarse columnar dendrites growing epitaxially along the deposition direction of as-deposited Inconel 718 superalloy change to the coarse and non-uniform equiaxed grains due to recrystallization. With the dissolution of Laves phase and precipitation of a large number of strengthening phase γ″ and γ′, the tensile mechanical properties in three mutually directions increase substantially. The tensile properties of tested specimens whose tensile directions are parallel with the base plate reach the tensile properties standard of wrought Inconel 718 superalloy. There are also tested specimens whose tensile mechanical properties in the direction perpendicular to the base plate not meeting the tensile properties standard of wrought Inconel 718 superalloy.