The effect of heat treatment on tensile and creep properties of nickel-base superalloy, Inconel 718 in room and at high temperature was investigated. Solution treatment was applied on the as-received material at 980oC for 1 hour before water quenched followed by double aging treatments at 720oC and 621oC for 8 hours, respectively and then cooled in air. The tensile strength at elevated temperatures of 550oC and 650oC were slightly deteriorated for heat treated and as-received materials. Beside strength, significant difference was observed in the elongation. The elongation of heat treated samples drastically reduced to 4 to 5% only compared to that of the as received materials which exhibited more than 30% elongation. The significant increased in tensile strength is suspected due to the present of γ’, γ” and δ precipitates which pinned the movement of grain boundary and sliding. However, the present of these precipitates caused the material to become harder and brittle. Moreover, the increase in load from 70% to 90% UTS and in temperature significantly accelerated the creep rate.