The　size　effect　of　reinforced　concrete　(RC)　members　is　mainly　caused　by:1)the　heterogeneity　and　the　mechanical　nonlinearity　of　concrete;　and　2)the　complex　mutual　effect　between　steel　rebar　and　the　surrounding　concrete.The　influencing　factors　on　the　size　effect　of　RC　members　(e.g.RC　columns)　include　slenderness　ratio,reinforcement　ratio　and　the　grade　of　concrete　strength,etc.A　total　of　18　geometrically　similar　RC　columns,the　maximum　cross-sectional　size　of　which　was　600mm×600mm,were　conducted.The　failure　behavior　of　the　RC　columns　subjected　to　axial　compressive　loading　was　studied　and　the　influencing　factors　on　the　size　effect　of　nominal　axial　compressive　strength　were　analyzed　and　discussed.The　investigation　indicates　that,1)the　bi-logarithmic　plots　of　nominal　axial　compressive　strengths　for　large-scale　RC　columns　follows　closely　the　＇size　effect　law　(SEL)＇　proposed　by　Baant;　2)the　size　effect　of　nominal　axial　compressive　strength　becomes　more　pronounced　with　the　increase　of　slenderness　ratio,the　decrease　of　reinforcement　ratio　and　the　increase　of　the　grade　of　concrete　strength.　©　2018,　Science　Press.　All　right　reserved.