The precipitates at grain boundary in a directionally solidified Ni base superalloy after heat treatment, aging at 975℃, and creep rupture test have been characterized.Besides the primary MC carbides and fine particles of μ phase, the Re-containing M23C6 was observed.The precipitation kinetics revealed that the formation of M23C6 was associated with the dissolution of μ phase and MC carbides.TEM image shows that the continuous precipitation of M23C6 particles effectively hinders the dislocation movement and strengthens the grain boundaries.The high strength of the alloy suggests that M23C6 carbides are beneficial to the properties although Re as an important matrix strengthening element was consumed.