The paper presents the results of an analysis of the influence of technological parameters of pneumatic shot peening technology on the selected properties of a surface layer of butt joints made with Friction stir welding (FSW) method. Butt joints made of two 2024 – T3 aluminum alloy sheets with the thickness of 1 mm were shot peened with glass beads. The experiments were carried out according to the statistical 3-level completed plan PS/DC 32. Technological parameters were changed in the range: pressure p = 0.4 – 0.6 MPa and peening time t = 1-3 min. As a result of the conducted research, adequate equations describing the effect of the analyzed parameters on the surface roughness were obtained. Shot peening with glass beads reduced significantly the surface roughness from Ra = 5.2 µm to Ra = 1.42 µm. This treatment provides high compressive residual stresses and the increase of the surface layer hardness. The results show that shot peening is a highly efficient and cost-effective mechanical treatment used for improving mechanical properties of butt joints made with FSW method.