The creep deformation of three single crystal Ni-based superalloys with various Ru contents has been investigated to clarify the effect of Ru additions at very high temperatures and low stresses conditions. The creep properties were significantly improved by Ru additions under the conditions of 1150°C/100MPa and 1180°C/70MPa. It is noted that obvious γ′ phase dissolution occurs during the entire creep deformation at very high temperatures. It differs from the typical high-temperature creep curves that a short incubation period occurs before the primary creep stage during the creep deformation at very high temperatures. Ru additions are able to produce denser interfacial dislocation networks and improve the stability and homogeneous configuration of interfacial dislocations; and promote the high-temperature stability of γ′ phase and formation of perfect γ′ rafting. It is thus shown that Ru additions reduce the minimum creep rate, and prolong the secondary creep stage accordingly. The topological inversion of γ/γ′ microstructure did not occur under both conditions. The origin of the rapid increase of creep rate is closely relevant to the unstable propagation of micro-cracks in the vicinity of porosity in necked regions.