The aim of this study was to investigate the effect of tool tilt angle on friction stir welding ( FSW) of polyethylene ( PE). The samples were longitudinally butt welded with double passes of rotating cylindrical shouldered tool in a milling machine for different tool tilt angles. The welding parameters had significant effects on tensile properties and fracture locations of the welds. The tensile strength decreased with increasing tool tilt angle. The thickness of the welding zone decreased with increasing tool tilt angle which affects the tensile strength. The interface line between weld passes was formed shorter for the higher welding speeds because of the less effect of the frictional heat.