The deformation behavior of Inconel718 at room temperature was studied by tensile tests. Three kinds of specimens were tested, including cold rolled, heat treated with grain size ASTM5 and heat treated with grain size ASTM7. The true stress-strain curves were obtained based on the tensile test records. The true stress-strain relation can express the room temperature deformation behavior, which can be described by equations similar to the Voce equation. The limit value of the work-hardening rate theta(0) is very sensitive to the microstructure of the alloy.