Friction stir welding (FSW) is a relatively new, state-of the-art solid state joining process. This metal joining technique is derived from the conventional friction welding. In a typical FSW, a rotating cylindrical pin tool is forced to plunge into the plates to be welded (i.e. work piece) and moved along their contact line. During this operation, frictional heat that is generated by contact friction between the tool and work piece softens the material. The plasticized material is stirred by the tool and forced to “flow” to the side and the back of the tool as the tool advances. As the temperature cools down, a solid continuous joint between the two plates is then formed. Because the highest temperature in the FSW process is lower than the melting temperature of the work piece material, FSW yields fine microstructures, absence of cracking, low residual distortion and no loss of alloying elements that are the main advantages of this solid phase process. Nevertheless, as in the traditional fusion welds, a softened heat affected zone and a tensile residual stress parallel to the weld also exist. In this context we have applied this technique to weld Al-Al, Cu-Cu and Al-Cu couples. We studied the effect of experimental parameters like rotational and transverse speed on welding of above metals and consequent microstructure at interface and mechanical properties especially hardness and tensile strength. We obtained intact interface and high mechanical strength for all three couples at the rotational speed ranges from 600-1000 rpm and transverse speed from 40-80 mm/min.