The semi-oval hollow section, which is composed of one semi-circular flange, one flat flange and two flat web plates, is a recently emerged cross-section type. Currently, there is no structural design guidance for this cross-section due to the lack of investigation. This paper herein presents the experimental investigation of cold-formed steel semi-oval hollow section columns. The test program comprised tensile coupon tests, geometric imperfection measurements, five fixed-ended stub column tests and nine pin-ended short column tests. The ultimate load-carrying capacities, full load-displacement responses and failure modes of the test specimens are presented. Since the current design rules do not cover the semi-oval hollow sections presented in this study, the experimental results were only compared against design strengths predicted by the Direct Strength Method, in which the design equations were originally calibrated by cold-formed steel open sections with flat elements, to assess its applicability to the semi-oval hollow section columns.