AbstractFew studies have investigated the eccentric compression behavior of fiber-reinforced polymer (FRP) confined reinforced concrete (RC) columns. In particular, the studies on the eccentrically loaded large-sized FRP-confined RC columns are limited. In this study, the mechanical responses and size effect behavior of FRP-confined RC square columns under eccentric loading will be investigated experimentally and numerically. Nine carbon fiber–reinforced polymer (CFRP) confined columns and three control columns with cross-sectional widths (h) from 200 to 600 mm will be tested, in which the influence of the structural size and eccentricity ratio (e/h0) will be studied. The failure patterns, load–deflection responses, and nominal stress–strain curves of CFRP and longitudinal reinforcement will be presented. The nominal axial strength and corresponding lateral deflection of tested CFRP-confined RC columns size effect existed. Subsequently, a finite-element (FE) model was developed and verified, in which the mesoscale structure of the concrete was considered. The experimental results are supplemented by FE modeling with a wider range of structural sizes and e/h0. In addition, the predicted equation for nominal axial strength for eccentrically loaded CFRP-confined RC columns will be established, of which the accuracy will be verified by comparison with the experimental and numerical data.