Retaining ring for electric generator is required to have non-magnetism, high strength, high ductility and stress corrosion cracking (SCC) resistance. Several kinds of materials for non-magnetic retaining ring have been developed and recently 18%Mn-18%Cr austenitic steel which has been developed to improve susceptibility to SCC of 18%Mn-5%Cr austenitic steel has begun to use. 18%Mn-18%Cr steel contained high nitrogen content has been investigated as the material with high strength, high ductility and SCC resistance. On the base of the fundamental studies of chemical composition and cold work on increasing yield strength of 18%Mn-18%Cr steel, a trial 18%Mn-18%Cr retaining ring with yield strength 1400 MPa was successfully manufactured and mechanical properties, fatigue strength, fracture toughness and SCC were investigated for the trial ring material.