In this study, AA 6063 (AlMgSi0.5) aluminium alloy plates were welded by friction stir welding, a solid state welding procedure. The aim of this study is to investigate the influence of the process parameters on the microstructure, mechanical properties and low cycle fatigue behaviour of this particular alloy. Three different rotation and welding speeds have been selected, which makes a total of nine different welding conditions. Depending on the welding parameters, void-free and void containing welds have been obtained. A great majority of the specimens have broken in the region between the HAZ and the TMAZ. The weld mechanical properties are observed to be about 70 % of those of the base metal. About a 40 % decrease has been detected in welded specimens in terms of low cycle fatigue life.