The recent arrival of carbon fibre-reinforced polymer (CFRP) into the construction industry has attracted structural engineers and architects. CFRP is generally applied for concrete structures to increase the strength. Recently, this technology is extended to strengthen the steel structures. This paper presents the behaviour of CFRP-strengthened steel circular hollow sections (CHSs) under axial static loading and axial cyclic loading. It also investigates the axial strength variation of CHS in two different orientations (one and two layers of longitudinal and transverse) of CFRP and three different slenderness ratios (30, 35 and 40). The failure modes, load–deformation and load–strain behaviour of CFRP-strengthened CHSs are also presented in this paper. From the experimental results, it was found that the axial capacity of CFRP-strengthened CHS was enhanced up to 39% in case of static loading and 41% in case of cyclic loading compared with the unstrengthened specimen. Test results clearly demonstrate that the application of CFRP on steel hollow section increases the axial capacity, ductility and stiffness relative to the unstrengthened specimen. © 2015, King Fahd University of Petroleum & Minerals.