Abstract: The precipitation of secondary phases in single-crystal Ni-based superalloys with different contents of Re are investigated using TEM and SEM.The results show that after full heat treatment, the size of secondary gamma' phase decreases gradually with increasing Re content. During long-term thermal exposure at 1093 degrees C, some needle-like and rod-like secondary phases precipitate from the gamma matrix. With increasing Re content and prolonging of the thermal exposure, the amounts of precipitated phases clearly increase. In the alloy with 2.5 wt-% Re, the needle-like phases are identified as M6C carbides. In the alloy with 3 wt-% Re, both M6C carbides and mu phase are found. In the alloy with 15 wt% Re, the needle-like and rod-like precipitated phases are identified as mu and P phases. Stacking fault was found in the P phase and that part was identified as mu phase by SAD; that is, there is intergrowth of P and mu phases.