In the process of plastic bending of thin-walled profiles, there is a significant deformation of the cross-section, which has a very significant impact on the course and effects of the process of shaping construction products. In this paper experimental, analytical as well as numerical analyses of the box profile bending process have enabled to establish relationships determining the dependence of the cross-sectional form and bending moment on the bending curvature. The following paper discusses pure bending moment and the cross-sectional deformation of 21.5x21.5x1.8 mm and 25x25x2.5 mm square tubes made of the 6060 aluminium alloy. Satisfactory agreement of the experimental results and numerical calculations was obtained for the values of horizontal and vertical wall deflection, as well as for the experimental, calculated and numerical bending moment characteristics.