Cold-formed steel (CFS) is a steel-based material that is used in construction as a building material. CFS is made by rolling, pressing, and bending processes at ambient temperature which is classified as different process of production when compared with hot-rolled steel. CFS with a variety of shapes, grades, and cross-sections is studied to propose as a structural element in construction such as beams and columns due to its advantages for example fast production, lightweight, and anti-corrosion. However, CFS with a thin surface and open-shaped section is exposed to structural failures and problems which could affect the whole structure and lastly the structure will collapse. Structural failures that have always been discussed are local buckling, distortional buckling, global buckling, and torsion. Besides, rubberwood dust which is collected from the sanding process of rubberwood in furniture industry factories is used as artificial aggregate in concrete. Rubberwood is categorised as a waste material which normally disposed of in a landfill area and creates a lot of environmental problems. With the intention to solve the problems, the CFS channel section with 50 mm of flange element, 100 mm of web element, 12 mm of lipped element, and 1.55 mm of thickness is selected and proposed a built-up section by attaching two CFS channel sections in a face-to-face configuration. Rubberwood is moistened with tap water, shaped into pellets, and lastly sintered in an oven to form rubberwood dust pellet which replace the coarse aggregate in concrete. Then, the built-up face-to-face CFS section is filled with concrete with rubberwood dust pellets and forms the sustainable composite structure. The main objective of the study is to determine the mechanical performance of rubberwood dust pellet concrete-filled built-up CFS stub columns and observe the failure mode of the structure. There are three parts of the experimental activity including the material performance of CFS, the chemical and physical rubberwood dust pellet, and the mechanical performance of built-up CFS column filled with rubberwood dust pellet concrete. From the testing and observation, the mechanical performance of the built-up CFS column filled with rubberwood dust pellet especially the ultimate load of the stub column increased by approximately 53.29% when compared with the stub column without concrete and decreased by about 23.31% when compared with the built-up CFS column filled with normal concrete.