Abstract: Round-ended rectangular concrete-filled steel tube (RER-CFST) members have been employed in bridge engineering. In this work, a total of eight RER-CFST specimens were designed and tested under lateral impact loading to investigate their impact-resisting performance. The dynamic responses of the specimens with various cross-section aspect ratios under different impact energies were obtained. Afterward, the finite element (FE) models were established by employing the ABAQUS software to analyze the mechanical mechanism during the whole impacting process and the influences of aspect ratio, steel ratio and impact velocity. Finally, the equivalent-single-degree of freedom (ESDOF) method was adopted to predict the maximum mid-span deflection of this type of member under a lateral impact. Results showed that the RER-CFST specimens mainly show global flexural deformations and exhibit good ductility. An obvious plateau stage was found in the impact force responses, demonstrating the obvious energy dissipation by global deformation. In addition, the impact-resisting performance of the specimen enhances with the increase of cross-sectional aspect ratio and steel ratio. The development of mid-span deflection of RER-CFSTs subjected to a lateral impact can be well predicted using the ESDOF method by considering the bilinear resistance function.