An experimental study was conducted to investigate the influence of FRP confinement on the buckling behavior of longitudinal steel reinforcing bars (rebars) in RC columns subjected to monotonic and cyclic axial compression. Test results of 12 FRP-confined RC columns and 12 FRP-confined plain concrete columns (control specimens) are presented with particular attention to the evolution of strains in the longitudinal steel rebars and the FRP jacket as the load increases. For an FRP-confined RC column subjected to monotonic axial compression, the contribution of longitudinal steel rebars to the overall axial load carried by the column was deduced by subtracting the contribution of the FRP-confined plain concrete from the total axial load. The test results showed that the compressive stress-strain response of longitudinal steel rebars in FRP-confined RC columns follows that from tensile testing before the axial stress reduces gradually due to the onset of buckling deformation. Significant interactions were found to exist between FRP confinement and the buckling of longitudinal steel rebars. This interaction should be carefully considered when formulating constitutive laws for both the longitudinal steel rebars and the FRP-confined concrete for use in theoretical modeling. (C) 2017 Elsevier Ltd. All rights reserved.