Abstract: The evolution and mechanism of γ′ phase growth in cast superalloy K480 and DD407 were studied during the ageing at 870 ℃ for 3 000 h. The results indicated that there were no TCP phase precipitating from matrix for both alloys, the γ′ phase coarsened slightly, but the γ′ phase grew faster in the DD407 alloy than in the K480 alloy. Generally, both alloys have good microstructure stability during long term ageing. With the increase of ageing time, grain boundary of K480 became broader, and carbides grew up along grain boundary, finally carbides chain formed and even gradually changed into carbides film. The relationship between of γ′ phase size and ageing time for K480 alloy followed the square law, while it followed the cubic law for DD407 alloy. The growth mechanism of γ′ phase for K480 and DD407 alloy were mainly controlled by interface and diffusion, respectively.