The microstructure and stress rupture properties of three experimental single crystal nickel superalloys with different Ti/Al ratios were investigated. The microstructure as-cast state and after heat treatment was analyzed by OPM and SEM. Partition ratio of alloy element in two phase and misfit degree were measured and analyzed by TEM with EDS. The results show that with increasing of Ti/Al ratio, the amount of g-g ￠ eutectic in interdendrtic region as-cast state increases slightly, the size of g ￠ phase in heat treated state decreases a little and the morphology turns regular and the misfit decreases. The change of Ti/Al ratio has no obvious effect on the transformation temperatures. The stress rupture life is improved gradually with increasing of Ti/Al ratio.