The　objectives　of　this　work　are　to　study　the　influence　of　structural　size　on　the　plastic　hinge　length　of　square　concrete-filled　steel　tubular　(CFST)　columns　and　to　discover　the　influence　of　confinement　generated　by　steel　tubes　on　the　plastic　hinge　length.　A　total　of　24　square　CFST　columns　were　designed　and　tested　with　different　column　widths　(i.e.,　200　mm　similar　to　800　mm)　and　different　confinement　effects　(described　by　width-to-thickness　ratio,　i.e.,　50,　80　and　100).　The　failure　behavior　and　the　curvature　distributions　of　the　tested　columns　subjected　to　axial　compression　loads　and　horizontal　cycling　loads　were　reported,　and　the　corresponding　plastic　hinge　lengths　of　the　columns　were　obtained.　The　test　results　indicate　that,　as　the　column　width　increases,　the　plastic　hinge　length　increases　linearly,　about　0.6-0.9　times　the　column　cross-sectional　widths.　Also,　as　the　confinement　effect　increases,　namely,　the　magnitude　of　the　width-to-thickness　ratio　decreases,　the　plastic　hinge　length　decreases　slightly.　Moreover,　the　non-dimensional　plastic　hinge　length,　defined　as　the　ratio　of　plastic　hinge　length　and　column　width,　was　proposed.　The　non-dimensional　plastic　hinge　length　decreases　with　increasing　the　column　width,　showing　a　significant　size　effect.　An　empirical　formula　for　predicting　the　magnitude　of　the　plastic　hinge　length　of　CFST　columns　was　established.