Abstract: In situ tensile tests with special designed SEM were conducted to trace the whole process of crack initiation and propagation till to fracture of Al₂O₃ seeded P/M Rene 95 Ni-base superalloy. The experimental results show that a non-metallic inclusion can induce crack initiation. When the inclusion size is larger than a certain critical size, the crack can propagate to be the main crack inducing the specimen to fracture. Consequentially, both the yield strength and the tensile strength of the specimen are remarkably decreased.