Abstract: The fatigue tests in 105-108 cycles of GH4169 Ni-based superalloy were carried out at ambient temperature by the ultrasonic fatigue tester, and then the S-N curve was obtained and the fatigue fracture morphology was observed. The results show that the S-N curve exhibited a descending trend and the fatigue limit was not observed. The fatigue fracture of the specimen still occurred when the number of cycles exceeded 107. The fatigue crack initiation positions didn′t show the regularity with the S-N curve descending. The fatigue cracks mostly initiated from the surface and few from internal of the specimen. Under the ultrasonic load the plastic and brittle failure modes were both found in the specimen.