Abstract A high-strength Fe/Al dissimilar joint was successfully fabricated by double-sided friction stir spot welding (FSSW) with adjustable probes. By this technique, a flat surface on both sides of the joint can be obtained due to the double-sided shoulders and probes. Strong mechanical interlocks were introduced by the adjustable probes in the welding interface. In addition, a continuous and uniform IMC layer with a thickness as thin as about 30 nm was formed at an extremely low rotation speed due to the fresh surface induced by the adjustable probes. Consequently, a high-strength welded joint can be fabricated. Nano-beam diffraction results revealed that the 30 nm IMC layer was composed of a ternary phase of Al–Fe–Si. This novel technique was demonstrated to be effective and productive for joining dissimilar materials.