Abstract: Two kinds of single crystal superalloys that have the same element content excerpt Al content, one containing 5.6 % Al and the other kind having 6.0 % Al, were casted in a directionally solidified furnace. The long-term aging of the alloys after heat treatment was performed at 1 040 ℃ for 800 h. Effects of Al content on the volume of eutectic, heat treatment microstructure and long-term aging microstructure of the alloys were investigated by SEM. The results showed that: with the increase of Al content, the volume of eutectic slightly increased in the as-cast microstructure; the size of γ′ phase in the dendrite core didn't change much but it slightly increases in the interdendrite zone; after long-term aging, the amount of TCP phase and the raft tendency of γ′ phase in the interdendrite zone both increased; the microstructure stability, the elongation and contraction area of the alloys decreased while the stress rupture lives of the alloys were improved.