In curent study, Properties of friction stir spot welding (FSSW) of Al-Cu composite produced by accumulative roll bonding ( ARB ), have been investigated. Four aluminum sheets with thickness of 500 µm were used to produce Al-Cu composite. Also Three copper sheets with the thickness of 100 µm were inserted between aluminum sheets. This produced sandwich, then rolled for six cycles. Finally Al-Cu composite with the thickness of 1 mm was produced. In welding process, effect of tool rotational speed, plunge depth of tool, and it's geometry on the properties of welds were investigated. After welding process, first the appearance of workpieces was examined. In very low tool rotational speeds -for example 560 rpm- because of low heat input, small fragments were chipped away from the workpiece.on the other hand, with increasing tool rotational speed- for example to 1400 rpm- Surfaces of sheets were squeezed because heat input increases in these speeds.welding with 710 and 900 rpm resulted in creation of soundness appearance of welds due to the moderated heat input produced by these rotational speeds during friction stir spot welding. different regions of joints such as stir zone, transitional zone and base metal were charactrized by using optical microscopy and scanning electron microscopy (EDS) equiped with chemical microanalyzer (EDS). Results showed that with increasing tool rotational speed, plunge depth of tool and using cylindrical pin , the volume of stir zone and it's essential length (d) were increased. The increment of these processing parameters resulted in sufficient heat input during friction stir spot welding process. Furthermore, due to the smaller frontal surface of the triangular pin, less pressure was applied by the pin face when plunging into the workpiece. This fact led to creation of smaller stir zone by using triangular pin rather than cylindrical pin. Increasing in the volume of stir zone and it's essential length led to increase the tensile shear force of the fractured joints welded with friction stir spot welding by applying these processing parameters. The material flow during friction stir spot welding of Al-Cu composite was investigated. This issue investigated by plunging the tool into different plunging depthes, before the shoulder contacted the surface of the upper sheet. results were compared joints that were welded by full plunging depth. Furthermore, existance of sufficient contrast between aluminum and copper layers asisted the analysis of material flow and finding movement direction of materials. Examination of material flow showed that several regions exist i the stir zone of welds due to different applied forces and heat input in this region. Weakness in creation of some part of the stir zone that have lower heat input or/and have weaker movement force resulted in decrement of the stir zone's volume or isolation of the base metal i the stir zone. This phenomenon occured during friction stir spot welding when using triangular pin. X-ray diffraction patterns showed that intermetallic compounds exist i the stir zone of welds. These phases were Al 2 Cu and AlCu 3 . Existance of these intermetallic compounds resulted in increasing hardness of the stir zone rather than base metal in the joints. Keywords: Friction stir spot welding, Al-Cu composite, Accumulative roll bonding, Intermetallic compounds