Friction stir spot welding (FSSW) of Al alloy 6016-T4 sheet was evaluated using a conventional pin (CP) tool and off-center feature (OC) tool. Tool rotation speed and plunge depth were varied to determine the effect of individual process parameter on lap-shear separation load. Maximum separation load of about 3.3kN was obtained by using a 0.2mm shoulder penetration depth with 1500rpm tool rotation speed for the CP tool and 2500rpm for the OC tool. Three different weld separation modes under lap-shear loading were observed: interfacial separation, nugget fracture separation and upper sheet fracture separation. Microhardness profile for weld cross section indicated no direct relationship between microhardness distribution and separation locations.