In　this　study,　a　total　of　six　geometrically　similar　normal-strength　RC　columns　of　different　structural　sizes　(in　the　ratio　3:5:7)　and　axial　compression　ratios　(0.4　and　0.6)　were　tested　to　investigate　the　flexural　behavior　and　size　effect,　where　the　cross-sectional　sizes　of　the　columns　ranged　from　300　mm　to　700　mm,　and　the　shear-span　ratio　was　4.　The　experimental　results　indicate　that　the　size　effects　in　the　flexural　behavior　of　RC　columns　under　monotonic　horizontal　loading　were　obvious,　including　the　bearing　capacity　of　specimens　and　their　ductility,　and　the　compression　strain　on　the　concrete,　which　decreased　with　increasing　cross-sectional　height.　The　larger　the　axial　compression　ratio,　the　more　obvious　the　size　effect　of　the　bending　bearing　capacity　and　ultimate　compression　strain　of　the　concrete.　When　the　axial　compressive　ratio　was　small,　the　size　effect　of　ductility　was　more　pronounced.　However,　the　assumption　of　a　plane　section　still　held　for　large-scale　specimens,　which　is　an　indication　of　no　size　effect.　Moreover,　there　was　no　obvious　size　effect　in　the　failure　patterns　besides　an　increase　in　the　crack　width　with　cross-sectional　size.　According　to　the　test　results,　a　size-related　model　that　considered　the　strength　coefficient　at　was　established　to　estimate　the　bending　bearing　capacity　of　RC　columns,　and　there　was　good　agreement　between　the　model　and　experimental　results.　We　found　that　a　bi-logarithmic　plot　of　the　strength　coefficient　a(1)　closely　followed　the　＂size　effect　law＂　proposed　by　Bazant.