Abstract: To study the microstructural stability of GH4169C alloy with high content of phosphorus and niobium, the microstruc-ture and hardness of GH4169C alloy and GH4169 alloy after long time aging were comparatively analyzed in this paper. These two su-peralloys were subjected to aging treatment at 600, 650, 704 and 720℃ for different times from 30 h to 10000 h. The microstructural evolution of the alloys was characterized by using a field emission scanning electron microscope and a Brinell hardness tester. The re-sults indicate that, at the service temperature of 650℃, GH4169 alloy and GH4169C alloy show excellent structure stability. Howev-er, above the service temperature, GH4169 alloy and GH4169C alloy have poor structure stability. In a short period of time, the two alloys lose stability. In contrast, the microstructure stability of GH4169C alloy is higher than that of GH4169 alloy with aging at 704℃, while GH4169C alloy shows a lower stability compared with GH4169 alloy at 720℃. It is thought that the stability of γ'phase in GH4169C alloy increases with increasing Nb and P contents. GH4169C alloy shows a better microstructure stability than GH4169 alloy at 704℃. However, the content of δphase will also increase with increasing Nb content, leading to the decrease in microstructure sta-bility of GH4169C alloy. At ultrahigh temperature (720℃), the microstructure stability of GH4169C alloy is inferior to GH4169 al-loy. This means that, compared with GH4169 alloy, the modified GH4169C alloy can be used in a higher temperature, whereas the temperature increase is limited, the microstructure stability of GH4169C alloy will decrease at ultrahigh temperature.