Aluminium alloys are established in the most demanding engineering applications because of good physical and mechanical characteristics. At the same time the development of new welding technologies enables joining of high-strength aluminium alloys, which are hard to weld by conventional fusion welding. This offers different researches of mechanical properties and circumstances in such weld joints. In the final project paper we therefore analysed longitudinal residual stresses in joints of dissimilar high-strength aluminium alloys 7075-T651 and 2017A-T451. With the friction stir welding procedure we successfully created six sample joints with different welding parameters. Further, in selected measuring points longitudinal residual stresses according to the welding direction were measured by the method of x-ray diffraction. On the basis of performed measurements we evaluated the distribution graphs of residual stresses and proved that the residual stresses in the stir-zone are positive, that is tensile. By moving away from the weld joint tensile residual stresses become compressive stresses. We also found out that bigger extremes of residual stresses are present on the retreating side and the highest values were measured in the specimen welded with the highest rotation rate.