High Strength Steel (HSS) box columns are usually fabricated from steel plates by welding. The welding process can introduce residual stresses and geometric imperfections into the sections and affect their strengths. In this study, an experimental investigation on the behavior of high strength steel box column under compression was carried out. In order to find out the effects of different welding process and heating treatments on the column strength, two different welding methods namely, Flux-Cored Arc Welding (FCAW) and Submerged Arc Welding (SAW) were employed. For each welding method, three different heat treatment conditions including As-Welded condition (AW), Preheating (PH) before welding and Post-Weld Heat Treatment (PWHT) were studied. The column strength under pure compression was studied by considering both initial geometrical imperfections and welding residual stress. The effects of different welding processes and heating treatment methods on built-up box column strength were investigated and discussed.