<p>This study investigates the flexural behaviour of cold-formed lean duplex stainless steel (LDSS) rectangular hollow beams with perforations provided at different locations along the length of the beam. Extensive finite element analysis is performed by incorporating material and geometric nonlinearities to determine the ultimate load carrying capacity of rectangular hollow beams with perforations at specific locations; i.e., close to support on the flange, in the middle third region on the web, and close to support on the web. The results obtained from the analysis has shown that the least effect towards the ultimate strength is; when the perforations are provided at flange—near support and the maximum reduction in strength is observed, when perforations are provided at web—near support. The ultimate moment capacity calculated using the finite element approach is compared with the current design rule for cold-formed steel members, the direct strength method (DSM). In addition, to improve the load carrying capacity, stiffeners are introduced to the beams with perforation in the web – near support and compared with DSM. Finally, a reliability analysis is conducted to evaluate the applicability of DSM for perforated LDSS rectangular hollow beams.</p>