Simulated transient tests and standard static mechanical property tests were performed on irradiated specimens of D9, a low-swelling, advanced austenitic stainless steel developed for fast reactor operation. Results of the transient tests were compared with existing data on 316 and HT9 stainless steels. The D9 alloy exhibited the same behavior attributed to the fuel adjacency effect (which is characterized by reduced strength and ductility as a result of cladding contact with oxide fuel) observed in 316 stainless steel. In the mechanical property tension and fracture toughness tests, D9 exhibited a slightly lower fracture toughness than either HT9 or 316 stainless steel. Comparison of tensile strengths indicated that irradiated D9 is stronger than HT9, but slightly weaker than 316 stainless steel. The D9 alloy exhibited a lower tensile ductility than either 316 stainless steel or HT9. The D9 transient and mechanical properties data are now available for computer code analysis of D9 as a fast reactor fuel system material.