Sound joints of a far apart property, pure aluminum and mild steel, dissimilar materials were obtained by friction stir spot welding (FSSW) solid state joining process. Sheets of 2 mm thickness were overlapped and fixed with a fixture device then welded. Welding parameters that produced the sound joint were identified. Joints microstructure and mechanical properties were investigated. A microstructural investigation has revealed a creation of mechanical interlocking and discontinuous formation of the intermetallic compounds found at the interface. The intermetallic compound (IMC) layer thickness ranged from 6 μm to 17 μm with the optimum condition specimen, 800 rpm and 5 Sec dwell time. Tensile–shear test showed that failure load has increased with increasing tool plunge depth and rotational speed. After the optimum value of rotational speed, the shear failure load decreased. The maximum shear failure load of 2.15 KN attained at 800 rpm and 2.4 mm plunge depth.