The effect of smooth tool pin eccentricity on mechanical properties and microstructure of 5 mm thick friction stir welded aluminum alloy AA5754-H24 was investigated. Three different tools were used in friction stir welding (FSW), cylindrical tool pin without eccentricity (T0), two cylindrical tool pin with eccentricity of 0.2 mm and, 0.8 mm (T2, T8) were used to weld AA5754-H24 aluminum alloy. The FSW was performed using tool rotation speed of 600 rpm and different welding speeds of 100, 200, 300, and 500 mm/min. After FSW the joints were investigated using tensile testing, hardness testing and optical microscopy. The use of FSW tool pin eccentricity 0.2 mm produces a friction stir weld joint with higher mechanical properties and finer precipitates. The tensile strength increases with increasing welding speed with maximum at 500 mm/min. However, the case is reversed in case of FSW tool pin eccentricity of 0.8 mm, the tensile strength decreases with increasing welding speed