Bimetallic transition joints using aluminum alloy 6061-T6 and stainless steel 304 L are useful in providing reliable stainless steel welds on nuclear components at temperatures below 200 °C, while maintaining the attractive radiation tolerance of the aluminum alloy. The mechanical performance of inertia welded Al6061-T6:304LSS transition joints was evaluated after neutron irradiation up to 3.45 dpa at 100 °C (maximum) in the High Flux Isotope Reactor to determine the viability of using these transition joints for nuclear and reactor applications. Neutron radiation produced moderate hardening ($\Delta$$\sigma$y≈90 MPa) with limited change in ductility. Tensile specimens were produced from multiple transition joints and no batch-to-batch variation was found. Tensile responses were found to align with typical responses of wrought Al6061-T6, indicating that the behavior of the joints was dictated by the Al6061-T6 section of the joint.