Abstarct: In this study, the friction stir processing (FSP) was used to produce an AA 5456-O mextal matrix composite reinforced with SiO2 nanoparticles. The parameters used in this process were the traverse speed of 16,8 mm/min and the rotational speeds of 2500, 1600, 800 rpm, and the amount of reinforcement used was 5, 10 and 15 wt. %. The size of the reinforcement was about 20 nm. By this process, it is possible to remove the casting defects and improve the microstructure of the mextals, thereby improving the hardness and ductility. In addition, the FSP method is used to homogenize and refine the microstructures and to increase the mechanical properties. Due to their unique properties, aluminum alloys have been remarkably developed, but one of the obstacles on the use of these types of alloys is the loss of their properties. For this reason, the mechanical properties can be improved by the addition of ceramic particles. 5xxx aluminum alloys usually have Al3Mg2 precipitates in their microstructures, which can act as boosters in the matrix. The microstructural studies were accomplished by the optical and the scanning electron microscopies. The results showed that the average grain size in the stir zone decreases by adding the reinforcing particles. The results also showed that the grain size decreases with decreasing the traverse speed. In order to investigate the mechanical properties, the tensile and microhardness tests were performed. It was observed that the hardness increased from 80 HV at the baxse mextal to 208 HV at the stir zone. The maximum tensile strength was obtained as 300 MPa for the sample processed by the traverse speed of 16 mm/min, rotational speed 800 rpm and 5 wt.% reinforcement.