The effect of Ru addition on the as cast microstructure, structural evolution during heat treatment and long term aging was employed in single crystal superalloys with different contents of Ru addition (0, 1?5 and 3?0 wt-%). The results show that NiAl based b phase can occur in the interdendritic region in 3Ru alloy. With increasing Ru content in the alloys, the incipient melting temperature of alloy decreases gradually, while the liquidus and solidus changed slightly. After solution treatment and the same aging treatment, the c9 phase size decreased with increasing Ru addition. An remarkable inverse partition of alloying elements, i.e. more matrix forming elements Re and Mo distribute to the c9 phase and more Ni element distribute to the matrix, was observed in the alloys with more Ru content after aging treatment. Ru addition can accelerate the rafting of c9 phase and suppress the precipitation of topologically close packed (TCP) phases effectively.