A comparative study on the influence of different manufacturing process on physical, chemical and mechanical properties of cold-formed, hot-formed and cold-formed with subsequent heat treatment steel square structural hollowsections manufactured to Grade S355J2H of BSEN10219 and BSEN10210was carried out. Physical propertieswere checked against the corresponding production standards. Chemical composition test using optical emission spectrometerwas employed to analyze their differences in chemical contents,while tensile test, sectioning test and hole-drilling test were carried out to analyze the difference in mechanical properties such as yield stress, tensile stress, ductility, impact toughness and locked-in residual stress. The study concluded that mechanical properties are greatly affected by their manufacturing process, and hot-finished sections are not the same as hot-formed sections although they shared the same production standard.