The effects of Ru on the microstructure and stress-rupture property were investigated in two experimental Ni-based single crystal superalloys with and without Ru addition(5.1%,mass fraction).The results indicate that the morphology ofγ’ precipitates in the dendrite core and interdendritic region are intermediate and nearly spherical,respectively,in the Ru-free alloy after being aged at 1100℃for 8 h.The Re partitioning ratio increases due to Ru addition and Ru partitioned preferentially to theγphase in both dendrite core and interdendritic region of the Ru-containing alloy,which results in more negative lattice misfit and more cuboidalγ’ precipitates.Meanwhile,theγ’ volume fraction increases while the precipitate size and y channel width decreases due to Ru addition in both dendrite core and interdendritic region.Ru addition improves the stress-rupture life at 1100℃/140 MPa significantly due to higherγ’ volume fraction,more negative lattice misfit and a well rafting structure as well as lessγchannel width. The effects of Ru on the microstructure and stress-rupture property were investigated in two experimental Ni-based single crystal superalloys with and without Ru addition (5.1%, mass fraction). The results indicate that the morphology of γ ’precipitates in the dendrite core and interdendritic regions are intermediate and nearly spherical, respectively, in the Ru-free alloy after being aged at 1100 ° C for 8 h. The Re partitioning ratio increases due to Ru addition and Ru partitioned preferentially to the gamma phase in both dendrite core and interdendritic region of the Ru-containing alloy, which results in more negative lattice misfit and more cuboidal gamma ’precipitates. While while the gamma’ volume fraction increases while the precipitate size and y channel width decreases due to Ru addition in both dendrite core and interdendritic region. stress-rupture life at 1100 ℃ / 140 MPa significantly due to higher γ ’volume fraction, more negative lattice misfit and a well rafting structure a s well as less gamma channel width