This paper deals with an experimental investigation on the friction stir welding of pure copper. 4 mm thick copper plates have been welded in the butt joint configuration using a conical unthreaded tool, with and without preheating. An electrically heated backing plate has been employed to increase the initial temperature of the plates and to investigate the influence of pre-heating on the weld ability of the considered material. The welded joints have been analyzed by means of macroscopic and microscopic observations, microhardness measurements and tensile tests. Obtained outcomes suggest that more complex pin shape is needed to promote an adequate material flow without pre-heating.