Abstract: Variation of microstructure and mechanical properties of LF9 alloy after aging at different temperatures was studied. The results show that with increasing the aging temperature, tensile strength both at room and high temperature of the alloy increased, plasticity and impact toughness decreased; the primary precipitated phases were γ′, M23C6 and MC after aging. The precipitated amount of the main strengthening phase γ′ increased with increasing the aging temperature. When the temperature was below 720 ℃, the amount increased signifcantly, while above 720 ℃,the amount increased stably. The aging temperature had little effect on the precipitated amount of M23C6 and MC phase. There was a linear relationship between average size of γ′ phases and the aging temperature.