In this study, AA7075-T651 aluminum alloy was joined by friction stir welding (FSW) method, using two different pin offset values, and the microstructure, macrostructure, mechanical properties of welded joints were examined. The tensile strength, elongation at rupture, and bending strength of welded joints were measured in the ranges of 236-408 MPa, 0.3-5.7 % and 110-574 MPa, respectively. Tensile test results revealed that the highest tensile strength of 408 MPa was obtained with the process parameters of 630 rpm tool rotational speed (TRS) and 0 mm pin offset. It is worth noting that joints, welded with a TRS of 800 rpm in the same manner, i.e., the pin was positioned at zero offset, exhibited the lowest tensile strength, with a value of 236 MPa. Microstructural and macrostructural observations revealed that welded joints exhibiting lower tensile strength and elongation at rupture consist of various types of defects (e.g. tunnel and cavity). Defect-free joints were fractured at a region between heat affected zone (HAZ) and base metal; however, welded joints with variety of defects were fractured through HAZ.