Abstract: The relationship between microstructural inhomogeneity and mechanical properties of the stationary shoulder friction stir welded (SSFSW) joint for 6061-T6 aluminum alloy was investigated. Results show that there is existing obviously microstructural inhomogeneity in the SSFSW joints, which reflected in the different grain size and shape, morphology and distribution of precipitates. It should be noted that the different precipitates is the major factor of the mechanical properties variation. Resulting from the microstructural inhomogeneity, the HAZ which is closed to the NZ was softened seriously, and its hardness and tensile strength were the lowest in the joint, reaching at 60% and 72% of the base metal, respectively. The strength and plasticity of the NZ are the best in the joint because of the precipitation strengthening and finegrain strengthening, and the tensile strength and elongation of the NZ reach at 88% and 215% of base metal, respectively. With the distance from NZ increasing, the ultimate tensile strength and yield strength of microtensile specimens increase, while the elongation of samples decreases.