In this study, AA 6013 aluminum plates were butt-welded with friction stir welding via pin offset technique. Macrostructural observations revealed that kissing bonds, originated from the broken oxide layers, were found to occur in the welded joints. The fracture location of welded joints after tensile tests was found to be outside the joint area, revealing that kissing bonds which were formed in the stir zone exhibited no detrimental effect on the mechanical properties of joints. Microstructural observations revealed that phases belonging to Mg2Si, Al4Cu2Mg8Si7 and Al (MnFe)Si were observed in the x-ray diffraction pattern of friction stir welded joints. The highest tensile strength with a value of 206 MPa was achieved with the process parameters of 1.5 mm pin offset towards the advancing side and 500 min 1 tool rotational speed, leading the ratio of tensile strength of joint to ultimate tensile strength of base metal, also known as joint efficiency, to reach 74 %.