In order to study the behavior of cold-formed thin-walled stainless steel built-up box section stub columns， a total of 25 fixed-ended stub columns including 14 built-up section specimens without holes， 6 unstiffened channel or edge-stiffened channel section specimens and 5 built-up section specimens with circular web holes were tested under axial compression. The material of specimens was S30408 austenitic stainless steel. The experimental results involving failure modes， ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The experimental results show that the type of built-up section has a significant effect on the ultimate bearing capacity of the built-up section column， in which the test specimens of CC-section and UU-section exhibit the largest and smallest bearing capacity respectively. The ultimate bearing capacity of built-up UU-section specimens is larger than the sum of the bearing capacity of the single channel section specimens. The holes on the web have almost no weakening effect on the ultimate bearing capacity of the specimens when the hole diameter-to-web height ratio is less than 0.5. The test results were compared with predictions calculated by the design method as per the current American Specification ASCE/SEI 8-22. It is found that the test strengths were lower than the predicted values， indicating that the current codified provision in ASCE/SEI 8-22 is not applicable to be directly used for ultimate bearing capacity predictions of the cold-formed thin-walled stainless steel built-up box section stub columns.