Abstract: In order to develop a good understanding of mechanical property of non-thin-walled cold-formed square hollow sections (thickness > 6 mm), the material tensile testing was carried out at various positions including flat, corner and flat-corner, considering different thicknesses, wides, forming techniques and steel grades. Compared with previously published research results, it was found that both the yield and ultimate strengthes at the corner were greater than those at the flat; and at the corner the increment of yield strength was greater than that of ultimate strength. The material strengthes at the flat-corner position were not significantly higher than those at the flat. Although both the yield and ultimate strengthes at all positions increased to some extent, the ratio of ultimate strength to yield strength and the elongation decreased meanwhile. the stress-strain curves of material presented gradual yielding development without obvious yield plateau. The strain-hardening modulus at the corner was significantly greater than that at the flat, and the strain-hardening modulus of the square hollow section fabricated through “circular first, square then” forming process was greater than that fabricated through “square directly” forming process. Based on the experimental results, the analysis model for the mechanical property of non-thin-walled cold-formed square hollow senctions was proposed.