Under　the　action　of　earthquake,　the　reinforced　concrete　(RC)　columns　may　subject　to　torsional　moment,　and　the　existence　of　torsion　will　change　the　failure　mode　of　RC　columns.　In　order　to　study　the　size　effect　of　RC　columns　on　pure　torsional　failure,　a　numerical　model　of　RC　columns　on　pure　torsional　failure　was　established　by　using　the　three-dimensional　meso-scale　numerical　simulation　method,　considering　the　meso-heterogeneity　of　concrete　and　the　bond-slip　action　between　reinforcements　and　concrete.　The　influence　of　structural　size,　longitudinal　reinforcement　ratio,　stirrup　ratio　and　cross-sectional　shape　on　torsional　failure　of　RC　columns　was　investigated.　The　results　show　that:　the　tested　RC　columns　show　brittle　failure　patterns,　the　nominal　torsional　strength　presents　obvious　size　effect;　the　longitudinal　reinforcement　presents　little　influence　on　the　size　effect;　columns　with　square　cross-section　present　stronger　size　effect　than　the　ones　with　circular　shape;　stirrups　can　improve　the　torsional　strength,　while　they　would　weaken　the　size　effect　on　torsional　strength.　Finally,　a　prediction　formula　for　nominal　torsional　strength　in　the　full-size　range　was　established　by　modifying　Bažant＇s　size　effect　law.　Copyright　©2022　Engineering　Mechanics　Press.　All　rights　reserved.