The effect of long-term aging on microstructure and creep properties of a single crystal Ni-based superalloy was investigated. The results show that the g ￠ phase remains cubic distribution after aging at 800 oC for 1000 h; the g ￠ phase gradually connects and rafts after aging at 980 oC for 1000 h or at 1010 oC for 500 h. The μ phase precipitates in the form of needles and granules when aged at 980 oC for more than 500 h or at 1010 oC for more than 100 h; the μ phase gradually increases with the aging time prolonging at 980 oC, while it first increases and then decreases when aged at 1010 oC. The creep lives of the alloy change a little after long-term aging at 800 oC, while the lives decrease with increasing of aging time and temperatures at 980 and 1010 oC.