Concrete-encased　concrete-filled　steel　tube　(CFST)　box　members　have　been　recently　used　as　piers　and　arches　in　bridges　owing　to　their　high　stiffness　and　strength.　However,　the　seismic　behavior　of　these　members　has　not　been　thoroughly　investigated,　which　hinders　the　usage　of　such　members　in　earthquake-prone　zones.　In　this　study,　eight　concrete-encased　CFST　box　specimens　and　eight　RC　box　counterparts　were　tested　under　constant　axial　load　along　the　specimen　and　cyclic　lateral　load　at　the　midspan.　The　experimental　parameters　were　the　axial-load　level　and　cross-sectional　type　of　the　column.　The　effects　of　these　parameters　on　the　strength,　ductility,　stiffness　degradation,　and　energy　dissipation　were　studied.　Compared　with　the　corresponding　RC　box　columns,　the　performances　of　concrete-encased　CFST　box　columns,　including　the　lateral　resistance,　stiffness　degradation,　ductility,　and　energy　dissipation　capacity,　were　significantly　improved.　A　simplified　calculation　method　was　proposed　to　evaluate　the　flexural　resistance　of　concrete-encased　CFST　box　columns.　©　2015　American　Society　of　Civil　Engineers.