In the present investigation, dissimilar AA1050-O and AA6061-T6 aluminum alloy plates were joined using friction stir spot welding (FSSW). The influences of tool rotational speed, dwell time and plugging depth on the tensileshear load of the friction stir spot welded (FSSWed) lap joints were studied. The FSSWed dissimilar plates were joined using a tool having a tapered pin profile and concave shoulder. The plates were joined using three tool rotational speeds of 710, 1120, and 1400 rpm, and three dwell times of 4, 7, and 10 seconds and three plugging depths of 2.95, 3.05, and 3.15 mm. The tool plunging rate was kept constant at 8 mm/min. The results indicated that the plunging depth has the most significant influence on the tensile-shear load of the welded joints followed by the tool rotational speed and the dwell time. The maximum tensile-shear load (5.32 kN) was obtained for weldments FSSWed at tool rotational speed, dwell time and plunging depth of 700 rpm, 10 seconds and 3.15 mm, respectively.