This　paper　presents　an　experimental　investigation　on　flexural　behavior　of　concrete-filled　aluminum　alloy　circular　hollow　section　(CHS)　tubes　under　pure　in-plane　bending.　A　total　of　28　circular　concrete-filled　aluminum　alloy　tubes　(CFAT)　with　nominal　concrete　cube　strengths　of　30　MPa　and　50　MPa　were　tested.　The　flexural　strengths,　failure　modes,　flexural　stiffness,　ductility,　bending　moment　versus　mid-span　deflection　curves,　overall　vertical　deflection　curves,　bending　moment　versus　longitudinal　strain　curves　and　longitudinal　strain　distribution　curves　of　circular　CFAT　beams　are　reported.　It　is　demonstrated　that　the　comparatively　large　wall　thickness　of　aluminum　alloy　CHS　tube　enhanced　the　bearing　capacity,　the　bending　deformation　capacity　and　the　ductility　of　circular　CFAT　beams.　Whereas,　the　concrete　strength　generally　has　insignificant　influence　on　the　flexural　strength,　flexural　stiffness　and　ductility　of　circular　CFAT　beams.　The　current　design　specifications　for　the　CFST　are　generally　inappropriate　for　circular　CFAT　beams　under　pure　in-plane　bending　with　high　scatter　of　predictions.　Further　research　is　still　required　to　propose　accurate　design　rules　for　circular　CFAT　beams.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.