Aluminum alloys are indispensable as a structural material in all branches of the transport industry. Their advantage over other metals is a favorable weight-to-strength ratio. Therefore, a new solid-state joining technology, friction stir welding intends to replace the existing technology (riveted joints) in the future. Mainly due to better weld quality and method simplicity. Due to the energy input during welding process, residual stresses are generated as consequence of microstructural and thermal modification. In the thesis, we wanted to figure out the effect of the mentioned welding technique on the residual stresses and mechanical properties of the welded joint. Measurements were compared at different weld zones, i.e. distance from the beginning of welding. At first, two plates of dissimilar aluminum alloys (2017A-T451 and 7075-T651) were joined by the method of friction stir welding. Then, before and after cutting-out specimens with water jet technology, we measured residual stresses in the transverse direction along the welding face. Our purpose was to study the effect of the energy input in different zones. Mechanical properties were measured using standard tensile specimens.We found the correlation between the compressive stresses on the face of the welded joint generated during the welding process and the tensile strength of the welded joint. Also, the highest tensile strength has been achieved at the specimen, which was cut out from the middle of the weld joint. There were the most optimal conditions.