Abstract: The influence of Ru element on the creep properties under 1120 ℃/140 MPa of high Re Ni-based single crystal superalloys with two levels of Ru (0, 2wt.%) additions was investigated. The γ/γ′ phase, partitioning ratio of alloying elements, deformation microstructures and the morphology of dislocations were studied by SEM, STEM/TEM and EDS. The results indicate that Ru addition results in decreasing the size of γ′ phase, width of γ channel and elemental partitioning ratio of Re，Mo and Cr which are important for the precipitation of TCP phase. Ru addition decreased the size of γ′ phase and width of γ channel, decreased the spacing of γ/γ′ interfacial dislocation networks and inhibited the precipitation of TCP phase in the process of creep loading, finally improving the creep properties of the investigatived alloy significantly. This study would be helpful for the understanding of ruthenium’s role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys. Key words: single crystal superalloys; Ru; micrstructures; partitioning of elements in γ/γ′ phase; creep properties